3 cups flour
1 tsp baking powder
1 1/2 tsp baking soda
1/2 tsp salt
1 stick (4 ounces) unsalted butter, softened to room temperature
1 1/2 cups sugar
3 eggs, separated
1 1/2 tsp vanilla extract
16 ounces sour cream
12 ounces chocolate chips (usually one package)
1/2 cup sugar mixed with 1 tsp cinnamon
Preheat your oven to 350 degrees, grease and flour a 9x13 cake pan.
Sift together the flour, baking powder and baking soda, and set aside. Whip the egg whites into stiff peaks, and set aside as well.
Cream together the butter and sugar until it's light and fluffy. Add the egg yolks and vanilla, and beat until well-incorporated. Gently mix half the sour cream into the batter, then half the flour mixture, then repeat with the remaining halves (being careful not to over-mix). Mix in about a third of the egg whites to lighten the mixture, then gently fold in the remainder, again being careful not to over-mix.
Pour half the batter into your prepared cake pan. Sprinkle on half the chocolate chips, and half the cinnamon-sugar mixture. Gently spread the remaining batter on top, and finish with the remaining chocolate chips and cinnamon-sugar. Bake until a tester comes out clean, ~40-50 minutes. Let cool slightly, then devour.