Spoiler:
Batter:
200 g butter or margarine
3 eggs
2 dl sugar
2 1/2 dl flour
1 dl cocoa
1 teaspoon baking powder
1 dl strong coffee
Frosting:
50 g butter or margarine
2 tablespoons hot coffee (I usually put a bit more to to make the frosting more fluid)
4 dl icing sugar
2 tablespoons cocoa
2 teaspoons vanilla sugar
Decorations of choice, for example nonpareils, crushed nuts or cocos flakes
Making the batter:
Melt the butter. Mix the flour, cocoa and baking powder into a single flour mix. Beat the eggs and the sugar into foam. Add the flour mix, melted butter and coffee, and mix. Pour the batter onto an oven pan with baking paper and bake for about 15 minutes in 200 C. Let it cool and start making the frosting.
Making the frosting:
Mix the other ingredients into soft butter, letting the hot coffee make the mixture fluid. (I often use a bit more than the 2 tablespoons indicated, to make the frosting suitably fluid.) When the baked brownie "mat" has cooled, pour the frosting on it and spread evenly with a knife.
Add the decorations of your choice and let the frosting get stiff. Cut the brownie "mat" into squares. The squares are even better if you put them in the fridge for a while before eating.