Brown the Butter. In a medium saucepan, melt 2 sticks of unsalted butter over medium heat, swirling occasionally until it becomes foamy and golden brown, about 5-7 minutes.

Combine Sugars. Pour cooled browned butter into a large bowl, add granulated sugar and dark brown sugar, mixing until smooth. Cool to room temperature.

Mix Dry Ingredients. In a medium bowl, whisk together all-purpose flour, bread flour, baking soda, baking powder, fine sea salt, and optional espresso powder until evenly blended.

Prepare Dough. Whisk eggs and yolk with vanilla extract into butter-sugar mixture until smooth, then gradually add dry ingredients and fold in chocolate and toffee.

Chill the Dough. Wrap dough tightly in plastic wrap and refrigerate for at least 24 hours to enhance flavors.

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

Shape and Bake. Use a 3-tablespoon scoop to portion dough onto sheets, spacing them 2 inches apart. Bake for 12-14 minutes until golden around edges.

Cool. Let cookies cool on baking sheets for 2 minutes before transferring to wire racks to cool completely.