(443g) sifted all-purpose flour* (spoon & leveled • baking powder 3/4 teaspoon baking soda • salt • (3sticks; 345g) unsalted butter softened to room • granulated sugar 3 large eggs, room temperature • large egg yolks, room temperature • pure vanilla extract • (360ml) buttermilk, room temperature* • unsalted butter, softened to room temperature • (540g) confectioners’ sugar • natural unsweetened or dutch-process cocoa powder • whole milk •