Perfected Yellow Cake

"Please read below the recipe for information on specific ingredients. I made and tested this cake over 16 times and have fine-tuned the ingredients and the methods. That isn't to say you aren't welcome to substitute and change, but in my yellow cake experience, this match up creates yellow cake perfection (substituting all-purpose flour, using cold eggs/milk, overly greasy soft butter, and a multitude of other factors can result in a dense, dry cake).If you are making your own cake flour using one of the two simple methods I posted about, don't worry about making one cup of cake flour at a time, instead, use 210 grams all-purpose flour and 45 grams cornstarch; sift twice. Then add the other dry ingredients and sift once more. For high altitude, add an additional 2 1/2 tablespoons cake flour before sifting (that would be about 2 tablespoons all-purpose flour and 1/2 tablespoon cornstarch if using a homemade cake flour substitute). Update: I've heard from several of you that while the cake tastes amazing, it is sinking in the middle or is baking flat. I can't analyze the why's too much because it will make my head pop off since I dedicated months of my life to this cake anyway. When I had too much leavening in the cake (2 teaspoons baking powder + 1 1/2 teaspoons soda), the cake rose too much in the oven and then deflated so I scaled it back to what worked perfectly for me. But here's the deal, if you are worried about sunken layers, increase the baking soda. My suggestion would be 1/2 or 3/4 teaspoon...."