Note: These recipes use NZ measurements. 1 c = 1 cup = 250 ml. 1 T = 1 tablespoon = 15 ml. 1 D = 2 teaspoons. 1 t = 1 teaspoon = 5ml. If you're in America, you may find you need a little extra baking powder in recipes that use it.
1/2T custard powder
1/2 c water
Melt butter in microwave. Then mix in sugar, custard powder and cocoa. Stir in water then microwave on high until thick.