For the cupcakes: Preheat oven to 180 Celsius. Mix the vinegar with the milk and set for 3 minutes. Sift the flour, cocoa, baking soda, baking powder and salt. Add the salt and mix. Incorporate the egg, the milk and vinegar mix, the oil and vanilla and integrate everything. Finally add the coffee dissolved in half a cup of hot water. Mix all the ingredients until there are no lumps.