01 - Place butter in a light-colored saucepan over medium heat. Melt and cook, stirring frequently, until butter foams and milk solids turn golden brown and fragrant, approximately 5–7 minutes. Pour immediately into a heatproof bowl and cool for 10 minutes.
02 - In a large mixing bowl, combine browned butter, brown sugar, and granulated sugar. Beat until smooth and glossy, about 2 minutes.
03 - Add eggs one at a time, beating thoroughly after each addition. Mix in vanilla extract and milk until fully incorporated.
04 - In a separate bowl, whisk together flour, baking soda, baking powder, and salt until well blended.
05 - Add dry ingredients to wet mixture and mix until just combined. Gently fold in chocolate chips and toffee bits, being careful not to overmix.
06 - Cover dough and refrigerate for at least 30 minutes, up to overnight, for optimal flavor and texture development.
07 - Preheat oven to 350°F. Line baking sheets with parchment paper.
08 - Scoop dough into 2-tablespoon mounds and place 2 inches apart on prepared baking sheets.
09 - Bake for 11–13 minutes until edges are set and lightly golden while centers remain slightly soft.
10 - Remove from oven and immediately sprinkle with flaky sea salt. Let cool on baking sheet for 5 minutes before transferring to wire rack to cool completely.