Ingredients:

  • 227 g unsalted butter, cut into cubes
  • 213 g packed dark brown sugar
  • 100 g granulated sugar
  • 50 g large egg, at room temperature (about 1 egg)
  • 18 g large egg yolk, at room temperature (about 1 yolk)
  • 15 g whole milk (1 tablespoon)
  • 9 g pure vanilla extract (2 teaspoons)
  • 281 g all-purpose flour (2¼ cups), spooned into the cup and leveled
  • 4 g baking soda (1 teaspoon)
  • 6 g fine salt (1 teaspoon)
  • 170 g toffee bits (1 cup)
  • 255 g semisweet chocolate chips (1½ cups)

Instructions:

  1. Melt the cubed butter in a light-colored skillet over medium heat, swirling the pan often, until it foams loudly and then the foam quiets down.
  2. Continue cooking until the milk solids on the bottom turn golden to amber brown and the butter smells like toasted hazelnuts. Do not let them turn black or smell sharp.
  3. Pour the browned butter and brown bits into a large mixing bowl. Let it cool for about 20 minutes, until warm to the touch but no longer hot.
  4. Add the dark brown sugar and granulated sugar to the cooled butter. Whisk for about 1 minute, until glossy and smooth.
  5. Add the whole egg, egg yolk, milk, and vanilla. Whisk for 1 to 2 minutes, until thicker and noticeably paler.
  6. In a medium bowl, whisk together the flour, baking soda, and salt.
  7. Add the dry ingredients to the wet mixture in two additions on low speed, mixing just until no dry streaks remain.
  8. Fold in the toffee bits and chocolate chips with a spatula. The dough should be thick and scoopable.
  9. Cover the bowl and refrigerate the dough for 1 hour.
  10. Scoop 3-tablespoon portions (about 55 g each) of chilled dough and place them on parchment-lined baking sheets, spaced about 2 inches apart. If the dough softens while scooping, return it to the refrigerator for 10 minutes.
  11. Preheat the oven to 180°C (350°F) with a rack in the center.
  12. Bake one sheet at a time for 11 to 13 minutes, rotating the pan halfway through, until the edges are deep golden and the centers look soft and slightly underdone. Repeat with the remaining dough, about 24 minutes of baking in total.
  13. Let the cookies rest on the hot baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.