Dry Ingredients:
- 7 ounces (1 ¼ cups + 2 T.) flour (high altitude: 7 ¼ ounces; 1 ¼ cups + 3 T.)
- 2 ounces (1/2 cup) unsweetened cocoa powder (high altitude: 2 1/8 ounces; ½ cup + 1 T. + ½ tsp.)
- 1 tsp. salt
- 1 ½ tsp. baking powder (high altitude: 1 tsp.)
Liquid Ingredients:
- 1 cup half-and-half (high altitude: 1 cup + 2 ½ T.)
- 1 T. vanilla extract
Creaming Ingredients:
- ¾ cup (1 ½ sticks) unsalted butter, room temperature
- 14 ounces (1 ¾ cups) extra-fine granulated sugar (high altitude: 13 ounces; 1 ½ cups + 2 T.)
- 4 eggs, room temperature (high altitude: 5 eggs)
Preheat oven to 350 degrees (335 for convection oven). Set the rack in the middle of the oven.
Measure the dry ingredients into a bowl and whisk to combine. Set aside. Measure the liquid ingredients into a separate bowl and whisk to combine.
In the bowl of a stand mixer (using the paddle attachment), cream together the butter and sugar on lowest speed until it starts sticking to the sides of the bowl. (This is a very important step. Be sure to do it on the lowest setting. It takes about 5 minutes for this step.) If using a vanilla bean, scrape out seeds and add to the creaming butter and sugar.
With mixer still on lowest speed, add the eggs one at a time followed by the yolk. Allow to fully incorporate after each addition. Stop the mixer and scrape sides of bowl.
With mixer still on low speed, add the dry ingredients and liquid ingredients alternating, beginning and ending with the dry ingredients. This should take about 60 seconds in total (3 to 5 steps of alternating adding). Don't wait for the ingredients to be fully incorporated before adding the next.
Stop the mixer and scrape the sides of the bowl. Mix on medium speed for 15 to 20 seconds.
Prepare the pans. For 9-inch-round cakes, grease and flour only the bottom of the pans; do not spray the sides. For cupcakes, grease or use cupcake liners (also lightly spray the top of the cupcake pan to help release any overflowing crowns). Deposit batter equally into each 9-inch round and smooth with spatula (for cupcakes, fill cups ~2/3 full). Bake 9-inch rounds for 28 minutes (high altitude: 35 minutes); cupcakes for 22 minutes (high altitude: 20 minutes). Test for doneness by inserting a toothpick into center of cake. Cake is done when there are just a touch of crumbs clinging to the toothpick. The cakes edges may pull away from the pan. Allow to cool to room temperature, 25-30 minutes, before carefully removing from pan. May be wrapped in plastic wrap and refrigerated for up to 5 days prior to frosting (not necessary, but if you are cutting it into a four-layer cake it will be much easier to work with when cold).