Put all of the ingredients except the cream of tartar and bicarb soda in a bowl.

Beat quickly and lightly for 3 minutes (I beat on setting 2 of my KitchenAid mixer for 3 minutes).

Add cream of tartar and bicarb soda and mix in lightly (I used setting 1 of my KitchenAid mixer for about 30 seconds).

Divide mixture evenly between two sandwich cake tins that are well-greased and have been lined at the bottom with baking paper.

Bake in a moderate oven (160 degrees celsius, fan-forced) for 18-20 minutes.

Allow to cool for a few minutes before carefully easing each cake from the tin. Use a knife if necessary to ease the cake from the sides of the tin.

Allow the cakes to cool on a wire rack that's covered with a clean tea towel.

Whip cream until nearly stiff.

Mix icing sugar, custard powder and milk to a smooth paste. Add paste to cream and continue beating until stiff.

Pipe the cream on the top of one sponge and then place the other sponge directly on top, like a sandwich. Push down very gently to secure the two cakes together.

Juice the lemon and then add the melted butter and half of the lemon juice to the icing sugar. Mix well and continue to add the juice a little at a time until the mixture reaches a runny consistency. Keep in mind that you want the icing to run slowly down the sides of the cake when judging whether the icing is the right consistency.

Add a little (or a lot) of lemon zest, depending on how lemony you'd like the glaze, and mix in well.

Put the cake on a wire cooling rack with a tray underneath to catch the icing run-off. Pour the icing over the cake and encourage it to run down the sides with a spatula if necessary. Use the run off below to ice the sides if there are any gaps remaining.

Decorate with edible flowers.