First, brown your butter. Add it to a sauce pan over medium heat and let it melt. It will start to crack and sizzle - let it do this while stirring occasionally. After five minutes or so, the butter will bubble up and calm down. When it does this, it is finished. Transfer it to a small bowl to let cool down a bit. About 5 minutes in the refrigerator.
While the butter is cooling, whisk together the flour, cornstarch, baking soda and salt. Set aside.
In a medium sized bowl, combine the melted and browned butter, brown sugar and granulated sugar and mix on medium speed until combined. Add the egg and vanilla extract and mix until combined. Add the dry ingredients and mix on low until a dough forms. Add your chocolate chips and stir them in until evenly incorporated. Cover the dough with tin foil or plastic wrap and let it chill in the refrigerator for one hour.
When the dough has 5-10 minutes left to chill, preheat the oven to 350 degrees Fahreinheit and line a baking sheet with parchment paper. Roll the dough and place them 2-3 inches apart on the baking sheet.
Bake for 9-11 minutes, flipping the pan half way through, until the edges are set and the cookies are golden brown. Let them cool on the pan for 5 minutes, then transfer them to a cooling rack to cool more. Enjoy while warm if you desire! Cookies will last for 4-5 days in an airtight container.