Softened unsalted butter for pans
3 3/4 cups all-purpose flour, plus more for pans
1 tablespoon baking powder
2 1/4 cups packed light brown sugar
1 teaspoon salt
2 1/4 cups half-and-half or whole milk
1 cup vegetable oil
1 tablespoon vanilla extract
3 egg whites
1/2 cup granulated sugar
2 cups butterscotch chips
• Preheat oven 350°F. Butter and flour one 10-inch, two 8-inch, and one 5-inch round cake pans. In a medium bowl, mix flour, baking powder, brown sugar, and salt. Add in half-and-half, oil, and vanilla and whisk until smooth.
• In a stand mixer, beat egg whites on high speed until stiff peaks form. Pour in granulated sugar and beat on high speed until glossy peaks form. Gently fold into batter and blend with whisk until smooth.
• Pour batter into prepared baking pans. Sprinkle butterscotch chips over top. Use a spatula or fork to gently submerge chips. Bake for 25 to 35 minutes, until a toothpick inserted into centers comes out clean. Remove cakes from oven and allow to cool for 10 minutes before removing from pans onto racks. Wrap in plastic wrap and chill until ready to assemble.
1/2 cup (1 stick) unsalted butter
3/4 cup packed dark brown sugar
1/2 cup heavy whipping cream
1 teaspoon vanilla extract
3 cups confectioners’ sugar
• Melt butter in a medium saucepan. Mix in brown sugar and heat over medium heat, stirring until smooth and creamy. Continue to stir just until mixture bubbles. Add in cream and stir vigorously for about 2 minutes. Remove from heat, add vanilla, and beat until well blended. Allow to cool for 10 minutes. Transfer to a stand mixer and beat in confectioners’ sugar, 1 cup at a time, until stiff peaks form.