Heat oven to 350 F.

Butter a 9×13 baking pan. If not nonstick coated, cover the bottom with a rectangle of parchment paper. Set pan aside.

In a large bowl, cream butter and 1 ½ cups sugar. Beat in egg yolks and vanilla.

Sift 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, beat egg whites until stiff, then fold into batter.

In a small dish, whisk together sugar and cinnamon for filling and topping.

Spread half the cake batter in the bottom of prepared pan. 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.

With the palm of your hand, ever-so-gently press the chocolate chips a bit into the batter. No need to submerge them, you just want to make sure they adhere a bit.

Bake for 40 to 50 minutes, rotating halfway through, until a tester inserted into the center of the cake comes out clean.