Pre-heat oven to 180 degrees celsius/355 degrees fahrenheit (fan forced).
Prepare two baking trays by greasing lightly and lining with baking paper.
Beat butter, icing sugar and vanilla extract together until the mixture reaches a pale colour.
Stir in sifted custard powder and flour using a butter knife or spatula.
Using floured hands, roll mixture into small balls (about 1 tablespoon full or 20 grams).
Place balls onto prepared baking trays, leaving room for biscuits to spread a little.
Flatten each ball slightly using a floured fork (making a fork pattern on the top of each biscuit).
Bake for 15 minutes or until the biscuits are firm to touch.
Allow to cool on the tray for 5 minutes before transferring to a cooling rack.
Filling
Once biscuits are completely cooled, make the filling.
Beat all ingredients together until the mixture is soft and fluffy.
Spoon about a tablespoon of filling mixture on the flat side of one biscuit and sandwich another on the top, flat side down. Gently squeeze together until the filling reaches the edges of the biscuit.
Notes
Storing: Filled, they should last a few days if stored in an airtight container in the fridge or a cool place. Unfilled, they should last a week and don't need to be stored in the fridge.Freezing: Freeze, wrapped well and placed into an airtight container, for up to 3 months. Nutrition: The nutrition information is an automatically generated estimate and is not guaranteed to be accurate.Note: This recipe makes 16 individual biscuits or 8 double biscuits.