Brown the Butter: In a medium saucepan over medium heat, melt 2 sticks of unsalted butter while stirring constantly. Watch as the butter begins to foam and then transforms into a golden brown color, developing a nutty aroma and dark bits at the bottom—this takes about 5-7 minutes. Once browned, remove it from heat to cool slightly.

Mix Sugars: Stir in ½ cup of granulated sugar and 1 cup of dark brown sugar into the hot browned butter using a whisk until thoroughly combined. The heat of the butter will dissolve the sugars beautifully. Allow the mixture to cool to room temperature, which should take about 15 minutes.

Combine Dry Ingredients: In a separate bowl, whisk together 1½ cups of all-purpose flour, 1 cup of bread flour, 1 teaspoon of baking soda, ½ teaspoon of baking powder, 1 teaspoon of fine sea salt, and 1 teaspoon of instant espresso powder (if using).

Combine Wet Ingredients: In the cooled sugar-butter mixture, whisk in 2 large eggs and 1 egg yolk, along with 2 teaspoons of vanilla extract. Combine until smooth. Then, gradually fold in the dry ingredients with a rubber spatula just until no flour streaks remain.

Add Chocolate & Toffee: Gently fold in 10 ounces of chopped semisweet chocolate and 1 cup of toffee bits into the dough until evenly distributed.

Chill Dough: Wrap the cookie dough tightly in plastic wrap and refrigerate it for at least 24 hours, but ideally up to 72 hours.

Bake Cookies: Preheat your oven to 350°F (175°C). Scoop 3-tablespoon portions of dough onto a lined baking sheet spaced 3 inches apart.

Final Bake: Place the baking sheet in the preheated oven and bake for 12-14 minutes. Keep an eye on the cookies; they should be golden around the edges but still soft in the center.

Cool: Allow the cookies to cool on the baking sheet for about 2 minutes before transferring them to a wire rack.