Preheat oven to 350.
Prepare a 9- by 5-inch loaf pan with butter and flour.
Cream butter and sugar until light and fluffy.
Sift flour, baking powder and baking soda. Stir into mixture, just until blended.
Stir in sour cream and vanilla until smooth. Add eggs and
mix until well blended.
Pour half of the batter into the loaf pan. Sprinkle half of the grated/chopped chocolate and cinnamon over the batter, reserving a small amount of the mixture to sprinkle over the top. Spread remaining half of batter over chocolate, then, using a knife, swirl the chocolate mixture into the batter. Sprinkle remaining chocolate and cinnamon mixture over top.
Bake cake in the preheated oven until a toothpick stuck into the center comes out clean, about 45–55 minutes.
Allow the cake to partially cool, then loosen with a knife from the sides and invert onto a rack to finish cooling.
This cake can be served fresh or frozen for another time.
Variation: For a purely vanilla pound cake, eliminate the cinnamon and chocolate.
Recipe Courtesy of Chef Jennifer Lewis, Illustration by Jessica Flores