Preheat the oven to 180° C. Sift flour and baking powder into a bowl. Add sugar, salt and butter. Mix everything to a crumbly mixture. Mix the eggs with the milk in a second bowl.
Pour the egg milk mixture and half of the coffee into the crumbly mixture while stirring. Stir until a smooth dough has formed. Chop the nuts roughly and mix in a bowl with some flour, then fold under the dough. Line the muffin trays with paper cups and fill them up to half the height with dough. Bake in a hot oven for 20-25 minutes until the cupcakes spring back to the touch of a finger. Remove and allow to cool completely.
For the icing; mix the icing sugar, butter, vanilla extract and the remaining coffee until creamy. Add the icing on to the cupcakes. Put half a walnut on each cupcake for decoration.