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

In a large mixing bowl, combine the flour, cocoa powder, granulated sugar, brown sugar, baking soda, baking powder, and salt.

In another bowl, whisk together the eggs, milk, vegetable oil, and vanilla extract.

Gradually add the wet ingredients to the dry ingredients and mix until just combined.

Fill each cupcake liner about 2/3 full with the batter.

Bake in the preheated oven for 15-18 minutes or until a toothpick inserted comes out clean.

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

In a mixing bowl, cream the softened butter until light and fluffy.

Gradually add the powdered sugar and cocoa powder, mixing well.

Add the milk and vanilla extract, mixing until smooth and creamy.

If the frosting is too thick, add more milk as needed to reach desired consistency.

Once the cupcakes have cooled completely, use a piping bag to frost each cupcake with the chocolate frosting.

Decorate with chocolate shavings or sprinkles if desired.

Serve and enjoy your delicious chocolate cupcakes!