Add the softened butter, brown sugar, and white sugar to a bowl. Use a stand mixer or hand mixer to mix for 2-3 minutes until well combined.

Add the egg yolk and vanilla extract and mix until combined.

Add the flour, cornstarch, baking soda, and salt. Mix until just combined.

Add the chocolate chips and stir until they?re evenly distributed through the dough.

Divide the dough in half and shape each half into a cylinder shape. Cover with plastic wrap and transfer to the freezer for 1 hour to chill.

When the dough is almost done chilling, preheat the oven to 350F.

Transfer the dough balls to a baking sheet lined with parchment paper. Bake for 10-12 minutes, until the edges are just set. Let them rest for 10 minutes on the baking sheet, then transfer to a cooling rack to cool completely.