Directions

1. Heat the butter in a skillet over medium-high heat. It will come to a boil. Continue cooking, stirring occasionally, until the solid particles at the bottom turn golden brown. Immediately pour into the bowl of a standing mixer to stop the browning. Let cool about 10 minutes.
   
2. Whisk together the flour, cornstarch, baking soda, and salt in a medium bowl.
   
3. Add sugar and brown sugar to cooled browned butter. Using the paddle attachment, turn on low speed to combine. Add in vanilla and eggs and turn machine on low until thoroughly combined.
   
4. Pour dry ingredients into bowl and turn on low speed until no streaks of flour remain. Take the bowl out of the mixer and add toffee. Gently fold toffee bits into the dough with a spatula.
   
5. Cover with plastic wrap, pressing the plastic down on the surface of the dough. Chill for at least 3 hours and up to 3 days.
   
6. Take dough out of the refrigerator, let sit at room temperature for about 30 minutes. Meanwhile, preheat the oven to 350° F and line a baking sheet with parchment paper.
   
7. Roll dough into balls, about 2 tablespoons each or 40 grams. Place 2 inches apart on baking sheet. Bake on the middle rack until the edges are set and just beginning to turn golden brown, about 9 minutes. The tops of the cookies should still be quite soft when you remove them from the oven, and may even appear slightly underbaked in the center. They will firm up while cooling.
   
8. Let cookies rest on baking sheet for 5 minutes, then transfer to a cooling rack. Store in an airtight container for up to 5 days.