Preheat the oven to 350°F. Line a cupcake pan with 12 liners and set aside.

In a small bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.

In a large bowl, cream the softened butter and granulated sugar with an electric mixer on high speed until fluffy, about 1-2 minutes.

Add the egg, egg yolk, and vanilla to the butter-sugar mixture. Mix on medium speed until pale and smooth, about 1-2 minutes.

Alternate adding the dry ingredients and the buttermilk to the mixture, mixing on low speed until just combined and smooth. Scrape down the sides of the bowl as needed.

Gently fold in the red gel food coloring until evenly combined.

Divide the batter among the cupcake liners, filling each about ¾ full.

Bake for 17-20 minutes, or until a toothpick inserted into the center comes out clean.

Let the cupcakes cool in the pan for 10 minutes, then transfer to a cooling rack to cool completely.

Beat the softened butter in a bowl with an electric mixer on high speed until pale and fluffy, about 5-10 minutes.

Add the cold cream cheese and mix on medium-high speed until well combined.

Gradually sift in the powdered sugar, mixing on low speed at first, then increasing to high speed until the frosting is smooth and fluffy.

Once the cupcakes are completely cooled, transfer the cream cheese frosting to a piping bag fitted with a decorative tip.

Pipe a generous amount of frosting onto each cupcake.

Decorate with sprinkles if desired.

Store leftovers in an airtight container for up to three days.