For the cupcakes
Using an electric whisk, beat the eggs and sugar until you get a frothy mix. Melt the butter in a small pan, and in the meantime, sift all the dry ingredients, namely the flour, potato starch, baking powder and ground coffee. This will result in an even lighter and fluffier batter. Brew the coffee and pour it into the frothed egg mixture. The rule is always the same: to obtain a smooth, creamy batter, add all the ingredients gradually and mix well. Dust the fresh blueberries with flour, sift to eliminate any excess, and add them to the mixture, stirring with a wooden spoon.
Pour the dough into the greased cupcake molds and bake at 180°C (356°F) for 30 minutes.
For the icing
The secret to a perfect cupcake is the icing. Prepare the coffee and let it cool. Once it is lukewarm, pour the coffee in a bowl with all the ingredients and froth the mixture using an electric whisk. Trust your eye: once the mixture becomes thick and smooth, put it into a pastry bag and enjoy decorating your cupcakes.