Preheat oven to 350℉ (177℃). Line muffin pans with cupcake liners. Whisk the flour, cornstarch, baking powder, baking soda, and salt together in a large bowl.
1 1/2 cups (212g) all-purpose flour, 1/4 cup cornstarch, 1 teaspoon baking powder, 1/4 teaspoon baking soda, 1/4 teaspoon salt
Beat the butter on high speed in a stand mixer or using a handheld mixer for 1 minute until creamy and light. Add sugar and beat another 2 minutes. Scrape sides and bottom of the bowl.
1/2 cup (113g) salted butter, 1 cup (200g) granulated sugar
Add eggs, vanilla and almond extract, beating on medium-high speed until combined. Beat in sour cream.
3 egg whites, 3 teaspoons pure vanilla extract, 1/2 cup sour cream, 1/2 teaspoon almond extract
Add the dry ingredients, mixing on low speed just until combined, then scrape the bottom and sides of the bowl.
With the mixer running on low speed, add the milk, stirring just until combined. Do not overmix.
1/2 cup whole milk
Fill each cupcake liner about 2/3 full with batter, then bake for 19-22 minutes, until a toothpick inserted in the center of a cupcake comes out clean.
Cool completely before frosting.