Step 1: Brown the Butter: Place the butter in a medium saucepan over medium heat. Melt the butter, then continue cooking while whisking constantly. The butter will foam, then turn clear, and finally begin to brown with small dark specks at the bottom. Once it smells nutty and looks golden-amber, remove it from the heat immediately and pour it into a large heat-proof bowl to cool for 15 minutes.
Step 2: Toast the Pecans: While the butter cools, place your chopped pecans in a dry skillet over medium heat. Toss them frequently for 3 to 5 minutes until they are fragrant and slightly darker. Set them aside to cool. Toasting the nuts is essential for the best crunch and flavor.
Step 3: Mix the Dry Ingredients: In a medium-sized mixing bowl, whisk together the all-purpose flour, baking soda, and sea salt. Ensure there are no large lumps so the leavening agent is distributed evenly throughout the dough.
Step 4: Combine Wet Ingredients: Add the dark brown sugar and granulated sugar to the bowl with the cooled brown butter. Whisk vigorously until well combined. Add the egg and vanilla extract, beating the mixture for about 1-2 minutes until it becomes slightly pale and smooth.
Step 5: Form the Dough: Slowly fold the dry ingredients into the wet mixture using a spatula. Mix until just combined; do not overmix. Gently fold in the toasted pecans until they are evenly distributed throughout the dough. For the best results, chill the dough in the refrigerator for at least 30 minutes.
Step 6: Bake the Cookies: Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. Scoop rounded tablespoons of dough onto the sheet, spacing them 2 inches apart. Bake for 10 to 12 minutes, or until the edges are golden brown but the centers still look slightly soft. Let them cool on the pan for 5 minutes before transferring to a wire rack.