chocolate chip sour cream coffee cake

Heat oven to 350°F (175°C). Butter a 9-x-13-inch baking pan and line the bottom with parchment paper. 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 eggs whites until stiff, then fold gently into batter.In a small dish, combine the cinnamon and remaining 1/2 cup granulated sugar for filling and topping.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 spoonfuls. 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. Bake for 40 to 50 minutes, rotating halfway through, until a tester inserted into the center of the cake comes out clean. Let cool in pan.Do ahead: I do *not* cover this when storing it (at room temperature because) I don’t want to lose the crackly top.