Instructions

• Preheat the oven to 350°F (175°C). Position a rack in the center of the oven. Grease a 13x9-inch baking pan and dust with flour, or spray it with a nonstick baking spray.
• In a medium bowl, whisk together the 4 large eggs, 2 large egg yolks, ½ cup buttermilk, and 1 tablespoon vanilla extract until combined. Set aside.
• In the bowl of a stand mixer, whisk together 2¼ cups cake flour, 1¾ cups sugar, 1¼ teaspoons baking powder, ¼ teaspoon baking soda, and ½ teaspoon salt until evenly mixed.
• Fit the mixer with the paddle attachment. Add the 8 tablespoons softened butter and ½ cup vegetable oil to the dry ingredients.
• Mix on low speed just until the fats are incorporated, then increase the speed and beat until the mixture is light in color and fluffy (about 1–2 minutes).
• Reduce the mixer speed to low and slowly pour the egg-buttermilk mixture into the mixer bowl, mixing just until incorporated.
• Scrape down the sides and bottom of the mixer bowl with a spatula. Beat on medium-high speed until the batter lightens in color and thickens, about 2–3 minutes.
• Scrape the batter into the prepared 13x9-inch pan and smooth the top with an offset spatula. Tap or rap the pan on the counter 2–3 times to release any large air bubbles.
• Bake in the preheated oven for 28–32 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs.
• Remove the cake from the oven and let it cool in the pan for 10 minutes. Then loosen the edges, transfer the cake to a wire rack, and cool completely.
• If you plan to use chocolate frosting (note: frosting ingredients are not included in the ingredient list), spread your prepared frosting over the completely cooled cake, then chill briefly to let the frosting set.