1. In a saucepan over medium heat, melt the butter and stir frequently. It will foam and then begin to turn golden with a nutty aroma. Remove from heat as soon as the milk solids at the bottom are golden brown. Let it cool for at least 20 minutes.

2. In a large bowl, combine the cooled brown butter, brown sugar, and granulated sugar. Beat until creamy, then mix in eggs and vanilla until smooth.

3. Whisk together the flour, baking soda, and salt. Slowly add the dry mixture to the wet mixture, stirring just until combined.

4. Gently fold in the toffee bits, being careful not to overmix.

5. Cover and refrigerate the dough for at least 1 hour. This helps deepen the flavor and prevent the cookies from spreading too much.

6. Preheat oven to 350°F (175°C). Scoop tablespoon-sized dough balls onto a lined baking sheet. Sprinkle with flaky sea salt if using. Bake for 10–12 minutes, or until edges are golden brown.