Preheat oven to 350º F. Line a 12-serving cupcake pan with paper or foil liners; set aside.

In a large mixing bowl, cream melted butter and sugar together until well combined, and sand-like.

Add eggs, one at a time, mixing until well incorporated.

Add vanilla and milk and beat just until combined.

Add flour, cocoa, baking powder, baking soda, and salt. Mix on low until well combined.

Pour in the hot water and mix until combined and batter is smooth.

Fill cupcake liners about ¾ full (approximately ¼ cup of batter).

Bake 20 – 22 minutes, or until toothpick inserted in the center of a cupcake comes out clean.

Allow cupcakes to cool completely before filling and frosting.

For the filling, scoop about the center of the cupcake, about 1 tablespoon worth of cupcake. Fill the center with chocolate hazelnut butter, or your favorite filling.

For frosting, cream butter and vanilla. Add cocoa and beat until combined. Add in powdered sugar one cup at a time, alternating with milk. Continue to beat with an electric mixer until smooth.

Frost the tops of the cupcakes.

Store in an airtight container for up to 4 days