Preheat oven to 350°F. Line a 12-count muffin pan with cupcake liners. This recipe makes 16-18 cupcakes, so you will have a few cupcakes to bake in a second pan or with a second batch.
With a handheld or stand mixer fitted with a whisk attachment, beat 2 egg whites (be sure to save the yolks for later) on high speed in a medium bowl until soft peaks form, about 2-3 minutes. Set aside.
Sift 1 1/3 cups flour and 1/4 cup cornstarch together to make sure it is evenly combined. Whisk this, along with 1/2 teaspoon baking soda, 4 teaspoons cocoa powder, and 1/4 teaspoon salt together in a medium bowl. Set aside.
Using a handheld or stand mixer fitted with a paddle attachment, beat 1/4 cup butter on high speed until smooth and creamy, about 1 minute.
Add 1 cup sugar and continue beating on high for 2 minutes until creamy. Scrape down the sides and the bottom of the bowl with a rubber spatula.
Add 1/2 cup oil and beat on high for 2 minutes. The butter may look “piece-y” and not completely combine with the oil, this is okay.
Add 2 egg yolks and 1 tablespoon vanilla. Beat on medium-high speed until combined. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed.
Beat in 1/2 teaspoon vinegar and the red food coloring– until you reach your desired color. I use about a tablespoon of gel food coloring.
Turn the mixer to low and add the dry ingredients in three additions alternating with the 1/2 cup buttermilk (add 1/4 cup buttermilk each time), beginning and ending with the dry ingredients. Mix just until each addition is incorporated. Do not overmix.
Fold the whipped egg whites into the red velvet batter with a rubber spatula. The batter will be silky and slightly thick.
Spoon a scant 2 tablespoons of batter into cupcake liners. Add a heaping tablespoon of cream cheese filing. Top with 2 more tablespoons of cupcake batter.
Bake for 20-25 minutes or until the tops of the cupcakes spring back when gently touched. Don’t overbake or your cupcakes will dry out.
Allow to cool in the pan for 5 minutes, then transfer to a rack to cool completely.
Top with cream cheese frosting.
I fill a piping bag with frosting and use my Wilton 1A tip for make frosting easy. Store in the fridge until ready to eat.