Start by melting butter in a pan and tossing in the pecans. Toast them until golden and fragrant, which usually takes about 5 minutes. Stir constantly to avoid burning and set aside to cool.
Melt the butter in a saucepan over medium heat until it turns golden brown with a nutty aroma. Scrape all the browned bits into a bowl—this is where most of the flavor comes from. Allow it to cool slightly before mixing with other ingredients.
In a large bowl, combine brown and granulated sugar with the browned butter using an electric mixer. Beat in eggs and vanilla extract until smooth. Gradually fold in flour, cornstarch, baking soda, cinnamon, and salt. Finally, fold in the toasted pecans.
Refrigerate the dough for at least 4 hours to help the cookies hold their shape. If you’re in a hurry, you can scoop and freeze dough balls until ready to bake.
Preheat oven to 375°F. Scoop dough onto a parchment-lined baking sheet. Press a pecan on top of each cookie if desired. Bake for 10–12 minutes, until edges are golden and centers are soft. Let cool slightly before transferring to a wire rack.