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Home » Recipes » Slices

Weetbix Marshmallow Slice

Published: Feb 25, 2023 · Modified: Oct 26, 2025 by Libby Hakim · 16 Comments

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This Weetbix Marshmallow Slice is one from the good ol' days, with a buttery weetbix base and a marshmallow topping that can only be described as luscious.

This slice is the less known but sweet and pretty cousin of the popular Chocolate Weetbix Slice.

A soft baked weetbix biscuit base is topped with sweet and fluffy marshmallow.

You can colour the marshmallow topping like I've done here or leave it white.

You can also top it with sprinkles, coconut, shaved chocolate... or again just leave it plain.

It's a lovely little slice recipe that's perfect for parties or to share at a morning tea.

Jump to:
  • The recipe for Weetbix Marshmallow Slice
  • Ingredients
  • How to make Weetbix Marshmallow Slice
  • Recipe tips and FAQs
  • Other retro slice recipe
  • Weetbix Marshmallow Slice

The recipe for Weetbix Marshmallow Slice

This recipe has been around for as long as I can remember, and I found a great version of it in this community cookbook from my mum's collection: Lourdes Hospital Recipe Book 2nd edition.

Lourdes Hospital is in Dubbo, NSW Australia. There's no date on the book, unfortunately, but I'd say it's from the 1970s or 80s at a guess.

My recipe here is based on the recipe in this book.

Ingredients

To make this slice, you'll need:

For the base

  • weetbix (or another similar wheat-based cereal)
  • brown sugar
  • butter
  • SR flour (or plain/all purpose flour + baking powder)
  • desiccated coconut.

For the marshmallow topping

  • sugar (caster or white)
  • water
  • gelatine (or substitute agar agar if you prefer a vegetarian option here)
  • pink food colouring (optional)
  • sprinkles or flaked coconut (optional).

Quantities for the ingredients can be found in the recipe card at the end of this post.

How to make Weetbix Marshmallow Slice

Making the base

Start by pre-heating the oven to moderate (180 degrees celsius, fan-forced).

Grease a slice tin (approx 28 x 18 x 3.5 cm) and line with baking paper, leaving excess on the sides to lift out slice once cooked.

Crush the weetbix into a bowl using your hands until fine and crumbly.

Add the remaining dry ingredients to the mixing bowl and stir to combine.

Melt the butter and add to dry ingredients. Mix well.

Press mixture into the prepared slice tin with your hands, evening the top surface using the back of a spoon.

Cook for 15 minutes.

Allow to cool before adding marshmallow topping.

Adding the marshmallow topping

To make the marshmallow, place the water, sugar and gelatine into a saucepan.

Place over low heat and stir to dissolve sugar and gelatine.

Bring to the boil and boil for 5 minutes. You should only need very low heat to boil – keep an eye on this so it doesn't boil over.

Let the mixture cool for half an hour before transferring the mixture to a mixing bowl and beating (starting on low speed and moving to high speed) for about 5 minutes or until mixture is light and fluffy.

Add the food colouring if you are opting to colour the marshmallow layer and mix again until the colour is even throughout mixture.

Pour onto top of the cooled base and use a plastic spatula to spread out evenly.

Add sprinkles or flaked coconut to the top of the marshmallow if you'd like.

Allow to set in the fridge for about 2 hours.

Lift slice from tray using the overhanging paper. Cut slice into squares using a sharp knife.

Recipe tips and FAQs

How do I get the timing right when making this slice?

Both the marshmallow and base need to cool for about half an hour before adding the topping.
If you make the marshmallow topping while the base is cooking, they should be both ready around the same time.
Once you take the base out of the oven, set your timer for half an hour. When the time is up, beat the marshmallow mixture as indicated and then spread it over the cooled slice.

How long will it keep?

Store slice in an airtight container in the fridge for up to 5 days.

Other retro slice recipe

There are plenty more recipes where this one came from! Here's a selection to get you started (or check out the entire slice collection here):

  • chinese chews
    Chinese Chews
  • rice bubble slice.
    Rice Bubble Slice
  • jelly slice sitting on timber board
    Jelly Slice Recipe
  • custard slice on plate dusted with icing sugar.
    Custard Slice
weetbix marshmallow slice.

Weetbix Marshmallow Slice

Libby Hakim
A retro slice that's deliciously sweet, soft and easy to make
5 from 6 votes
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Prep Time 10 minutes mins
Cook Time 20 minutes mins
Total Time 30 minutes mins
Course Dessert
Cuisine Australian
Servings 24 squares
Calories 144 kcal

Equipment

  • 1 slice tin (approx 28 x 18 x 3.5 cm)
  • stand mixer or handheld mixer

Ingredients
  

Base

  • 3 weetbix, crushed (or 50 grams of another similar wheat-based cereal)
  • ½ cup brown sugar
  • 190 grams butter
  • 1 cup SR flour, sifted (130 grams) (or same weight of plain/all purpose flour + 2 teaspoons baking powder)
  • ¾ cup desiccated coconut (60 grams)

Marshmallow Topping

  • 1 cup sugar (caster or white)
  • 1 cup water
  • 1 tablespoon gelatine (or substitute agar agar if you prefer a vegetarian option here)
  • 2-3 drops pink food colouring (optional)
  • 2-3 tablespoons sprinkles or flaked coconut (optional)

Instructions
 

Base

  • Pre-heat oven to moderate (180 degrees celsius, fan-forced).
  • Grease a slice tin and line with baking paper, leaving excess on the sides to lift out slice once cooked.
  • Crush weetbix into a bowl.
  • Add remaining dry ingredients to bowl and stir to combine.
  • Melt butter and add to dry ingredients. Mix well.
  • Press mixture into slice tin with hands and even the top surface using the back of a spoon.
  • Cook for 15 minutes.
  • Allow to cool before adding marshmallow topping.

Marshmallow Topping

  • Place water, sugar and gelatine into a saucepan. Place on low heat and stir to dissolve sugar and gelatine.
  • Bring to the boil and boil for 5 minutes. (You should only need very low heat to boil)
  • Let cool for half an hour before transferring to a mixing bowl and beating (starting on low speed and moving to high speed) in a stand mixer or with electric handheld beaters for about 5 minutes or until mixture is light and fluffy.
  • Add food colouring if you are opting to colour the marshmallow layer and mix again until colour is even throughout mixture.
  • Pour onto top of cooled base and use a plastic spatula to spread out evenly.
  • Add sprinkles or flaked coconut to top of marshmallow if you're opting to add these.
  • Allow to set in the fridge for about 2 hours.
  • Lift slice from tray using the overhanging paper. Cut slice into squares using a sharp knife.
  • Store slice in an airtight container in the fridge.

Notes

Q. How do I get the timing right when making this slice?
Both the marshmallow and base need to cool for about half an hour before adding the topping.
If you make the marshmallow topping while the base is cooking, they should be both ready around the same time. Set your timer for half an hour and when the time is up, beat the marshmallow mixture as indicated and then spread it over the cooled slice.
Q. How long will it keep?
Store slice in an airtight container in the fridge for up to 5 days.

Nutrition

Calories: 144kcalCarbohydrates: 18gProtein: 1gFat: 8gSaturated Fat: 6gPolyunsaturated Fat: 0.3gMonounsaturated Fat: 2gTrans Fat: 0.3gCholesterol: 17mgSodium: 55mgPotassium: 29mgFiber: 1gSugar: 13gVitamin A: 201IUVitamin C: 0.04mgCalcium: 8mgIron: 0.4mg
Tried this recipe?If you love it, let me know!

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Comments

  1. Susan Vincent says

    November 08, 2025 at 6:15 pm

    5 stars
    This recipe was made regularly when my brother and I were children. My mother was a very good cook of anything. However, she died young and I have missed her for 46 years. Now my family are enjoying this blast from my past! Love it. Thanks.

    Reply
    • Libby Hakim says

      November 10, 2025 at 11:37 am

      Hi Susan. Oh, so pleased that the slice recipe can bring back memories of your dear mum's wonderful cooking - and you can share it with the family. Enjoy x

      Reply
  2. Helen says

    November 02, 2025 at 9:48 pm

    yes yummy

    Reply
  3. Julie says

    October 23, 2025 at 7:04 pm

    Do you mix while in pot or transfer marshmallow mix into another bowl to mix?

    Reply
    • Libby Hakim says

      October 26, 2025 at 1:29 pm

      Hi Julie - transfer to a mixing bowl (if using handheld electric beaters) or the bowl of a stand mixer before beating. Thanks for the question - I've updated the post to clarify.

      Reply
  4. K says

    June 13, 2025 at 5:18 pm

    it doesn't actually say how many marshmallows??

    Reply
    • Libby Hakim says

      June 16, 2025 at 9:38 pm

      You make the marshmallow - see the recipe card at the end of the post.

      Reply
  5. Julia says

    August 14, 2024 at 6:41 pm

    Have you actually made this with agar agar as per your suggestion ? I would desperately love it to work but it doesn’t .. what do you do to make agar work ? Cheers

    Reply
  6. Kim says

    December 29, 2023 at 4:43 pm

    5 stars
    Awesome recipe. I had no detailed method in my book. Many thx. How much sugar does one need per recipe

    Reply
    • Karen Lindsay says

      March 16, 2024 at 8:58 pm

      1cup

      Reply
  7. Deborah says

    December 10, 2023 at 7:10 pm

    Hello, have you ever tried making this with cornflakes instead of Weet-bix? Thanks

    Reply
    • Libby Hakim says

      December 11, 2023 at 8:26 am

      Hi Deborah - I haven't but I'm sure it would be lovely!

      Reply
  8. PJ says

    April 29, 2023 at 9:52 pm

    Can this be made with gluten free wheatbix?

    Reply
    • Libby Hakim says

      April 30, 2023 at 9:16 pm

      Hi PJ - I imagine it would work fine however haven't tested it myself. Happy cooking!

      Reply
  9. Pat says

    April 07, 2023 at 9:50 am

    5 stars
    I've been making this since 1970 love it...

    Reply
    • Libby Hakim says

      April 07, 2023 at 10:22 am

      It's just one of those slices you never get tired of! Thanks for leaving your rating and review, Pat 🙂

      Reply
5 from 6 votes (3 ratings without comment)

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Hi, I'm Libby, a recipe collector and writer. I love everything about home cooking and share modern classics and recipes that have been passed down for generations – I hope you find a few that bring back treasured memories.

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