25 g butter
25 ml freshly brewed strong coffee, preferably espresso
200 ml icing sugar
2 tbsp cocoa powder
1 tsp vanilla sugar

Mix together the icing sugar, cocoa powder and vanilla sugar. Melt the butter in a small saucepan and mix in the coffee.

Add the dry ingredients through a sieve and mix until thoroughly blended. Immediately spread or pour the icing on a cake, brownies, muffins, doughnuts, pastries, etc, and let cool until set.

Recipe source: Finnish school home economics lesson recipe.