The most extraordinary moist Vanilla Sheet Cake made by preheating oven to 350°F greasing and lining 9×13 pan whisking 3 cups flour 2 tsp baking powder 1/2 tsp baking soda and 1/2 tsp salt beating 1 cup softened butter medium-high 1 minute adding 2 cups sugar beating 2 minutes light and fluffy adding 3 room temperature eggs and 2 extra yolks one at a time beating thoroughly then 1 tbsp vanilla on low alternating flour in 3 additions with 1 cup buttermilk in 2 additions beginning and ending with flour mixing just combined pouring into pan smoothing top baking 30 to 35 minutes until toothpick clean and edges barely pulling cooling completely at least 1 hour then beating 1 1/2 cups room temperature butter 3 minutes pale and fluffy adding 5 cups sifted powdered sugar one cup at a time adding 3 to 4 tbsp cream 2 tsp vanilla and salt beating medium-high 3 minutes incredibly light spreading over cooled cake in dramatic swoops. A completely perfect moist buttermilk vanilla sheet cake recipe.