Brown the Butter: Melt 2 sticks of unsalted butter in a medium saucepan over medium heat, stirring occasionally. Cook until golden brown and nutty, about 5 to 7 minutes. Remove from heat and cool to room temperature.

Combine Sugars: In a large bowl, combine cooled browned butter with ½ cup granulated sugar and 1 cup dark brown sugar. Whisk until creamy, about 2 minutes.

Whisk Dry Ingredients: In a separate bowl, whisk together 1 ½ cups all-purpose flour, 1 cup bread flour, 1 teaspoon baking soda, ½ teaspoon baking powder, and 1 teaspoon fine sea salt.

Mix Wet Ingredients: Add 2 large eggs and 1 egg yolk to the butter and sugar mixture along with 2 teaspoons of vanilla. Whisk until smooth.

Combine Mixtures: Gradually fold the dry ingredients into the wet mixture until just combined. Fold in 10 ounces of chopped semisweet chocolate and 1 cup of toffee bits.

Chill Dough: Wrap the dough tightly in plastic wrap and refrigerate for 24 to 72 hours.

Preheat Oven: Preheat your oven to 350°F (175°C) and line two baking sheets with parchment.

Shape Cookies: Portion the dough into balls using a 3-tablespoon scoop and place them on the sheets, spacing 2 inches apart.

Bake: Bake for 12 to 14 minutes or until lightly golden around the edges but still soft in the center.

Finish: Sprinkle flaky sea salt before removing from the oven and let them cool on the sheets for five minutes before transferring to wire racks.