01 - Melt unsalted butter in a medium saucepan over medium heat, stirring frequently. Cook until butter foams, develops a golden hue, and emits a nutty aroma, 5 to 7 minutes. Pour browned butter and solids into a large mixing bowl, allowing it to cool for 15 minutes.
02 - In a separate medium bowl, thoroughly whisk together all-purpose flour, baking soda, baking powder, and fine sea salt.
03 - Add packed light brown sugar and granulated sugar to the cooled brown butter. Beat until mixture is cohesive. Incorporate eggs one at a time, ensuring each is fully blended before adding the next, then stir in pure vanilla extract.
04 - Gradually blend the dry ingredients into the wet mixture until just combined. Gently fold in toffee bits and chocolate chips, if using.
05 - Cover the dough and refrigerate for at least 20 minutes, or up to 24 hours, to minimize cookie spread.
06 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
07 - Portion dough with heaping tablespoons, using approximately 2 tablespoons per cookie. Place dough balls at least 2 inches apart on prepared baking sheets.
08 - Bake for 11 to 13 minutes, or until cookie edges are golden and centers appear slightly underbaked.
09 - Let cookies cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely.