Good-Cooking - Black Walnut Cake

Ingredients

• 1/2 cup butter
• 2 cups firmly packed brown sugar
• 3 egg yolks, beaten
• 3 teaspoons baking powder
• 2 cups all-purpose flour
• 1/2 teaspoon salt
• 2/3 cup milk
• 1 teaspoon vanilla extract
• 1 cup black walnuts, finely chopped
• 3 egg whites, stiffly beaten