Directions

1. Heat oven to 350 degrees F. Butter a 9 x 13 inch baking pan and line the bottom with parchment paper.

2. In a large bowl, cream butter and 1 1/2 cups granulated sugar. Beat in egg yolks and vanilla. Whisk flour, baking soda, baking powder, and salt together into a separate bowl. Alternately mix in sour cream and then dry ingredients into butter mixture until both are used up and the batter is smooth and very thick. In a medium bowl with clean beaters, beat egg whites until stiff, then fold gently into batter.

3. In a small dish, combine the cinnamon and remaining 1/2 cup granulated sugar for filling and topping.

4. Spread half the cake batter in the bottom of prepared pan and spread smooth. Sprinkle with half of cinnamon-sugar mixture and 1 cup of chocolate chips. Dollop remaining cake batter over filling in spoonful's. Use a rubber or offset spatula to gently spread it over the filling and smooth the top. Sprinkle batter with remaining cinnamon-sugar and remaining chocolate chips.

5. Bake for 40-50 minutes, rotating halfway through, until a tester inserted into the center of the cake comes out clean. Let cool in pan.