Preheat your oven to 350°F (175°C) and prepare a cupcake tin by lining it with paper liners.

In a large mixing bowl, combine the all-purpose flour, unsweetened cocoa powder, granulated sugar, baking powder, baking soda, and salt. Whisk them together until thoroughly blended.

In a separate bowl, whisk together the eggs, milk, vegetable oil, and vanilla extract until fully combined and slightly frothy.

Gradually pour the wet mixture into the bowl with the dry ingredients, gently folding them together until just combined.

Spoon the batter into the prepared cupcake liners, filling each about two-thirds full. Bake for 18-20 minutes, or until a toothpick inserted comes out clean.

Remove the cupcakes from the oven and let them cool in the pan for 5 minutes before transferring to a wire rack to cool completely.

Beat the unsalted butter until creamy, then gradually add powdered sugar and heavy cream, mixing until well combined.

Divide the buttercream into several bowls and add gel food coloring to create vibrant hues.

Using a piping bag fitted with a star tip, pipe the colorful buttercream onto the cooled cupcakes, swirling colors for a beautiful effect.

Sprinkle with edible glitter and stars to finish the cosmic look.