Preheat the oven to 350 F (177 C). Prepare 4, 8-inch round cake pans with parchment paper circles and cooking spray. If you don’t have four pans, bake in batches. [Note 1]
In a medium mixing bowl, whisk together the sifted flour, cocoa powder, baking powder, and salt. Set aside. [Note 2]
2 ⅔ cups all-purpose flour, 1 cup cocoa powder, 1 tablespoon baking powder, ½ teaspoon salt
In a separate large mixing bowl, beat the softened butter, oil, and sugar together until smooth and light. Add the eggs, vanilla extract, and peppermint extract. Mix until well combined.
½ cup unsalted butter, ½ cup vegetable oil, 1 ½ cups granulated sugar, 4 large eggs, 1 teaspoon peppermint extract, 1 teaspoon vanilla extract
Gradually add the dry ingredients, alternating with the milk, starting and ending with the dry ingredients. Mix until just combined. Be careful not to overmix. The batter will be slightly thick, but still pourable. [Note 4]
1 ½ cups milk
Divide the batter evenly among the prepared cake pans. Bake for 20-25 minutes, checking for doneness by inserting a toothpick into the center of the cakes. It should come out clean. Start checking the cakes at 18 minutes to avoid overbaking. [Note 5]Let the cakes cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.