01 -
Preheat oven to 350°F (175°C). Line a standard 12-cup muffin tin with paper cupcake liners and set aside.
02 -
In a liquid measuring cup, whisk together 1/2 cup milk and 1/2 cup sour cream until smooth. Allow to reach room temperature.
03 -
In a medium bowl, whisk together 1 1/2 cups all-purpose flour, 2 tablespoons cornstarch, 1/2 teaspoon baking powder, 1/4 teaspoon baking soda, and 1/2 teaspoon salt.
04 -
In a stand mixer bowl, beat 1/2 cup unsalted butter on medium speed until smooth. Add 1 cup granulated sugar and continue beating until light and fluffy, about 2-3 minutes.
05 -
Add 2 large eggs one at a time, mixing well after each addition. Scrape down the bowl and mix in 2 teaspoons vanilla extract.
06 -
Add the dry ingredients in three additions, alternating with milk-sour cream mixture, beginning and ending with dry. Mix until batter is just combined.
07 -
Divide the batter into two bowls. In one bowl, stir together 1 tablespoon cocoa powder, 1 tablespoon milk, and 1-2 teaspoons red food coloring. Fold this cocoa mixture into one portion of batter until evenly tinted red.
08 -
Add 1 tablespoon plain batter to each liner, then 1 tablespoon red velvet batter, then another tablespoon plain batter. Gently swirl with a toothpick or skewer. Fill liners about two-thirds full.
09 -
Bake for 18-19 minutes, until a toothpick inserted into the center of a cupcake comes out clean. Cool in pan 5-10 minutes, then transfer to a wire rack to cool completely.
10 -
In a large bowl, beat 8 ounces cream cheese and 1 cup unsalted butter until smooth and fluffy. Add 1 pound confectioner’s sugar and a pinch of salt in stages, beating to fully incorporate. Mix in 2 teaspoons vanilla extract. Beat on high for 2 minutes until frosting is light.
11 -
Split frosting in half. In one half, mix in 1 tablespoon cocoa powder and 1-2 teaspoons red food coloring until smooth. For the marbled effect, fill a piping bag with both frostings side by side.
12 -
Once cupcakes are completely cool, pipe marbled cream cheese frosting onto each cupcake using a large piping tip.