In a medium sauté pan over medium heat, melt the butter while swirling occasionally until browned, about 5-7 minutes. Pour into a mixing bowl.

Add granulated and dark brown sugar to the cooled butter and stir until fully combined. Let cool to room temperature.

In a separate bowl, whisk together the all-purpose flour, bread flour, baking soda, baking powder, fine sea salt, and espresso powder (if using).

Stir in eggs and yolk, along with vanilla extract into the sugar mixture. Gradually add the dry ingredients until fully incorporated, then fold in chocolate and toffee bits.

Wrap the dough in plastic wrap and refrigerate for at least 24 hours, up to 72 hours.

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

Scoop dough onto prepared baking sheets, spacing about 2 inches apart. Optionally, freeze scooped dough for later.

Bake for 12-14 minutes or until edges are golden brown while centers remain soft.

Sprinkle with flaky sea salt if desired. Cool on sheets for 2 minutes before transferring to wire racks.