Preheat oven to 350F. Line two baking sheets with parchment paper and set aside.
In a small bowl, combine the flour, cornstarch, baking soda, baking powder, and salt. Set aside.
In the bowl of a stand mixer, add the butter and peanut butter and beat for about 1 minute until creamy and smooth.
Add the brown and white sugars and beat again for 1-2 minutes until pale and fluffy.
Add in the egg and vanilla and give it a quick whip to combine.
Add the flour mixture little by little, beating just until combined.
Pour the chocolate chips in and stir until evenly distributed.
Using a 2 inch cookie scoop, measure out cookies and place 2 inches apart on prepared baking sheets. Top with a few more chocolate chips.
Place in the oven and bake for 10 minutes or until edges are golden.
Remove from the oven and let them sit on the tray for 5 minutes and then transfer to a wire rack to cool. Top with flaky sea salt if desired.