Preheat oven to 350°F (180°C). Grease and line two 8-inch cake pans with parchment paper
In a large mixing bowl, beat together butter, sugar and egg yolks until fully combined. Scrape down the sides of the bowl as needed.
½ cup unsalted butter, 2 cups granulated sugar, 3 large eggs
In a small bowl, mix together oil, cocoa powder, red food coloring and vanilla extract. Whisk until smooth.
¼ cup vegetable oil, 3 tablespoons unsweetened cocoa powder, 1 to 2 teaspoons red gel food coloring, 1½ teaspoons vanilla extract
Add cocoa and oil mixture to the butter, sugar and egg mixture. Beat until all ingredients are fully incorporated and uniform in color.
Add the buttermilk and flour mixture to the bowl in three parts, alternating between buttermilk and flour.
1 cup buttermilk, 3 cups all-purpose flour
Add baking soda, salt and vinegar to the cake batter and mix to combine.
1 teaspoon baking soda, ½ teaspoon salt, 2 teaspoons white vinegar
In a separate bowl, beat egg whites until stiff peaks form. Gently fold in the stiff egg whites into the cake batter.
3 large eggs
Divide the batter evenly between the two cake pans and bake for 27 to 33 minutes or until the cake is risen, shrunk away from the sides of the pan, and springy to the touch. A toothpick inserted into the center of the cake should come out clean. Remove from oven and cool in pans for 15 minutes before inverting onto a cooling rack.