In a medium saucepan, melt the butter over medium-low heat. As the butter melts, it’ll start to foam, then turn a clear golden color. Continue to stir the butter, scraping up any browned specks from the bottom of the pan as it starts to brown. It should have a nutty aroma. Once browned and nutty, remove from the heat; set aside to cool slightly.

Whisk the flour, baking soda, salt, and cornstarch together in a medium bowl; set aside.

In a stand mixer fitted with the paddle attachment, beat the browned butter and both sugars together on medium speed until smooth and incorporated, about 1 minute. Add the eggs and vanilla and continue beating until combined, using a rubber spatula to scrape down the sides of the bowl as needed. Add the dry ingredients and mix on low until just incorporated. Stir in the chocolate chips/chunks with a wooden spoon.* Cover, and refrigerate dough for at least two hours, or up to three days.

Preheat the oven to 350ºF and line a baking sheet with parchment paper. Roll the dough into balls about the size of a golf ball, then place them on the baking sheet about 2 inches apart.

Bake for 9-10 minutes, or until the edges are set and the centers are puffy but still look slightly underdone. Allow cookies to cool on the baking sheet for 10 minutes before transferring to a wire rack to cool completely.