Add the softened butter and cookie butter to a mixing bowl.
Mix until smooth and creamy.
Add the powdered sugar and mix well.
Add the cream and mix until the buttercream becomes light and fluffy.
Add the vanilla extract and salt, then mix until smooth.
Transfer the buttercream to a piping bag and set aside.
Add the softened butter and powdered sugar to a mixing bowl. Mix until light and creamy.
Add the egg and egg yolk, then mix until smooth.
Add the vanilla extract and buttermilk, then mix well.
In a separate bowl, combine the all-purpose flour, cocoa powder, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture and mix until a smooth batter forms.
Add the hot coffee and mix until fully combined.
Divide the batter evenly among the lined cupcake cups.
Bake at 180°C (350°F) for 18–22 minutes, or until baked through.
Let the cupcakes cool completely, then make a small hole in the center of each cupcake.
Fill the centers with the Nutella cookie butter filling.
Pipe the prepared cookie butter buttercream over the cupcakes.
Serve and enjoy.
