Preheat the oven to 350 degrees F.
Grease and line two 9" cake pans with parchment paper.
Soak two cake strips in ice water. In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream the butter and sugar together until light and fluffy, about 2-3 minutes.
Mix in the egg yolks and vanilla until well combined.
Add half of the dry ingredients and mix on low speed until mostly combined. Then, mix in the buttermilk, yogurt, oil, vinegar, and red food gel, followed by the remaining dry ingredients.
In a separate small bowl, add the egg whites and use an electric hand mixer to beat until soft peaks form.
Using a rubber spatula, gently fold the whipped egg whites into the cake batter until fully combined.
Divide the cake batter between the prepared cake pans. Wrap the cake strips around the outsides of the pans.
Bake the cakes for about 30-35 minutes or until the edges start to pull away from the sides of the pan and a toothpick inserted comes out clean. Immediately turn the cakes out onto a wire rack to cool completely.
Once cool, wrap the cakes in plastic wrap and freeze until ready to decorate. (Frozen cake layers will be much easier to frost!)