For the Cupcakes:

Preheat oven to 350°F (175°C). Line a 12-cup cupcake pan with paper liners.

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

In a large bowl, cream softened butter and sugar with an electric mixer on high speed until light and fluffy (1–2 minutes).

Add the egg, egg yolk, and vanilla. Beat on medium speed until smooth and pale.

On low speed, alternate adding the dry ingredients and buttermilk until just combined. Scrape the bowl as needed.

Fold in red gel food coloring until evenly mixed.

Divide batter evenly between cupcake liners, filling each about 3/4 full.

Bake for 17–20 minutes, or until a toothpick comes out clean.

Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

For the Cream Cheese Frosting:

Beat softened butter on high speed for 5–10 minutes until fluffy.

Add cold cream cheese and beat on medium-high until smooth.

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

Assembling the Cupcakes:

Transfer frosting to a piping bag with your desired tip.

Pipe generously onto cooled cupcakes.

Decorate with sprinkles if desired.

Store leftovers in an airtight container for up to 3 days.