Step 1

Preheat the oven to 350 degrees (F). Line a 12-cup cupcake/muffin tin with cupcake liners and lightly spray the liners with non-stick spray, set aside.

Step 2

Place the butter in a large, microwave-safe bowl. Place the bowl in the microwave and melt the butter, heating it in 30 second increments, stirring in between each increment. Add in the oil and vanilla and whisk smooth. Add in the sugar and whisk until well combined. Add in the eggs and egg yolk, one at a time, beating well after each addition. Add the flour, cornstarch, cocoa powder, baking soda, baking powder, and salt to the wet ingredients and lightly combine them with a whisk before beating them into the mixture, stirring until it's just combined - be sure not to over mix here! Whisk in the apple cider vinegar and buttermilk and whisk smooth. Fold in the sour cream. Finally, stir in the food color, whisking the mixture just until combined.

Step 3

Divide the batter among the lined cupcake molds, filling each 3/4 of the way full (you will have enough batter for about 18 cupcakes). Bake for 15-17 minutes, or until a toothpick inserted in the center comes out clean. Cool completely before frosting.

Step 4

In a large bowl using an electric handheld mixer, beat the cream cheese, butter, and vanilla on medium-high speed until completely smooth; about 2 minutes. Reduce the speed to low and gradually add the sifted confectioners' sugar and salt. Once all of the sugar has been added beat on high-speed for 1-2 minutes. Once the cupcakes have completely cooled, spread the frosting over the cupcakes or use a piping bag to pipe it into decorative swirls. Store these cupcakes in the fridge, covered, for up to 3 days.