Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.

In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cocoa powder.

In a large bowl, beat together the granulated sugar, brown sugar, and softened butter until light and fluffy.

Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.

Gradually mix in the dry ingredients, alternating with the buttermilk, starting and ending with the dry ingredients.

Stir in the boiling water until the batter is smooth.

Fill each cupcake liner about two-thirds full with the batter.

Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.

Allow the cupcakes to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.

For the creamy chocolate filling, beat the heavy cream in a medium bowl until stiff peaks form.

In another bowl, beat the cream cheese until smooth, then gradually add the powdered sugar and cocoa powder.

Mix in the vanilla extract and gently fold the whipped cream into the cream cheese mixture until well combined.

Once the cupcakes are completely cooled, use a small knife or cupcake corer to remove a small portion from the center of each cupcake.

Fill each cavity with the creamy chocolate filling.

To make the frosting, beat the softened butter in a bowl until creamy.

Gradually add the powdered sugar and cocoa powder, mixing until smooth.

Add the milk and vanilla extract, beating until the frosting is light and fluffy.

Frost the filled cupcakes with the chocolate frosting, swirling it on top for a decorative finish.