For the biscuits:
55g icing sugar
55g cornflour (if you want to make ‘Yo-Yo’s’ instead, replace the cornflour with 55g custard powder)
½ teaspoon baking powder
For the filing:
30g butter (1 large tablespoon)
80g icing sugar (2 heaped tablespoons)
2 teaspoons boiling water
1. Preheat the oven to 180˚C and line two baking trays with baking paper.
2. Bring the butter to room temperature. Sift together the icing sugar, flour, cornflour (or custard powder), and baking powder.
3. Cream the butter until it is light and fluffy, then mix in all the dry ingredients to make a firm dough.
4. Take teaspoonfuls of the mixture and roll into little balls. Place them on the baking tray and flatten with a fork dipped in water.
5. Bake for 15-20 minutes, rotating after 10 minutes. Biscuits are cooked when they have spread a little, still very pale in colour, but are slightly browned on the bottom. Remove from oven and cool on a rack.
6. To make the filing, melt the butter in a small saucepan and add the boiling water. Pour this into the icing sugar and mix to form a smooth paste (we used slightly less water as we added food colouring to make the icing a purple colour).
7. Pair up the biscuits in matching sizes. Put about a teaspoonful on half of the biscuits. Put the partner biscuit on top of the icing and rotate slightly to encourage the filling to spread out to the edges.