Step 1: Brown the butter in a medium saucepan over medium heat until it smells nutty and golden brown bits appear at the bottom. Pour into a bowl and let it cool for 15 minutes.
Step 2: In a large mixing bowl, whisk the cooled browned butter with the dark brown sugar and granulated sugar until well combined and smooth.
Step 3: Add the egg and vanilla extract to the butter mixture, whisking vigorously for about 1 minute until the batter lightens slightly in color.
Step 4: Gently fold in the flour, baking soda, and sea salt using a spatula. Be careful not to overmix; stop once no dry flour is visible.
Step 5: Stir in the chocolate chips if using. Chill the dough in the refrigerator for at least 30 minutes.
Step 6: 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.
Step 7: Bake for 10-12 minutes or until the edges are golden but the centers are still soft. Sprinkle with flaky sea salt immediately after removing from the oven.