Preheat oven to 350°F. Grease and line a 9x9 inch baking pan with parchment paper.
In a large bowl, mix the flour, baking soda, baking powder, cornstarch, cinnamon, and salt. Set aside.
In another large bowl, combine the sugar, eggs, butter, vanilla extract, and sour cream. Beat with a hand mixer on medium speed for a minute, until just combined. Be careful not to overmix!
Add the dry ingredients to the wet ingredients and continue beating on high speed for 2-3 minutes, until the batter lightens in color and is very well combined.
Fold in the chocolate chips evenly.
Pour the batter into the prepared pan and evenly spread it. Sprinkle with chocolate chips and a bit of sugar (about 1 tablespoon).
Bake for about 35 minutes, or until a wooden skewer inserted into the center comes out clean.
Crack open the oven door, to let some of the hot air out. Remove the cake and let it cool before enjoying.
