1¼ cups dark brown sugar, packed
½ cup unsalted butter, softened
¼ cup shortening
2 large eggs
2 teaspoons vanilla extract
1¾ cups cake flour
3 tablespoons Dutch processed cocoa
1 teaspoon baking powder
½ teaspoon baking soda
½ teaspoon salt
1 cup sour cream (not fat-free)
4 egg whites
¼ cup sugar
Caramel frosting, see related recipe
Heat oven to 350 degrees. Lightly grease and flour, or line with parchment paper, three, 9-inch round, 1½-inch deep baking pans. Alternately, use 2 heavy duty 9-inch round, 2-inch deep baking pans.
In a large bowl, with mixer on high speed, cream dark brown sugar, butter, shortening and 2 whole eggs until light, about 3 minutes. Add vanilla and mix 30 seconds until smooth.
In medium bowl, combine cake flour, cocoa, baking powder, baking soda and salt. Whisk until even in color and cocoa is distributed. Add half of the dry ingredients to creamed butter/sugar mixture and mix on low speed for 30 seconds. Add ½ cup sour cream and mix 10 seconds. Add remaining dry ingredients and sour cream. Mix on medium speed for 1 minute. Scrape bowl well.
In a deep grease-free glass or metal bowl, whip the 4 egg whites until frothy, about 1 minute. Gradually add sugar to the whites and continue to whip until stiff peaks form. Gently fold the egg whites into the cake batter.
Divide between cake pans and bake until the center springs back when lightly touched. For three, 9-inch round pans, bake 15-20 minutes; for two deeper 9-inch round pans, bake 20-25 minutes. Cool completely before frosting.
To assemble cake: Spread a third of the frosting on bottom layer allowing dripping down sides. (Use half of the frosting for the deeper heavy-duty cake pans). Place second layer on top, pressing down gently to secure. Repeat with additional layer. Do not frost sides. Store at cool room temperature or refrigerate.
Nutrition values per serving: 343 calories, 26 g fat, 24 g carbohydrates, 1 g fiber, 5 g protein, 104 mg cholesterol, 151 mg sodium.