Preheat oven to 190 degrees C. Prepare baking dish.
In a large bowl, combine flour, sugar, cocoa, soda and salt.
Make a notch in the center and pour in beaten eggs, 1 cup of milk, water, vegetable oil and 1 teaspoon of vanilla. Mix well, fill out each form.
Bake in a preheated oven for 15 to 20 minutes. Allow to cool.
Make fillings: In a large bowl, whisk the butter and sugar, add a pinch of salt. Gradually pour 3 tablespoons of milk and 1 teaspoon of vanilla. Fill your cupcakes with a pastry bag.