In a medium pan over medium heat, melt the unsalted butter while stirring frequently. Keep an eye on it as it turns golden brown, about 5–7 minutes.

Stir in both granulated sugar and dark brown sugar until well combined. Let this mixture rest for about 10 minutes to cool down.

In a separate bowl, whisk together all-purpose flour, bread flour, baking soda, baking powder, fine sea salt, and instant espresso powder. Set aside.

Add large eggs and vanilla extract to the cooled butter mixture. Whisk until smooth, then fold in dry ingredients until no flour streaks remain.

Gently fold in the chopped semisweet chocolate and toffee bits until evenly distributed.

Wrap the cookie dough in plastic wrap and refrigerate for at least 24 hours.

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

Using a cookie scoop, form 3-tablespoon-sized balls of dough and place them on the baking sheets, about 2 inches apart.

Bake the cookies for 12–14 minutes until golden brown around the edges but still soft in the center.

Sprinkle flaky sea salt on top after removing from the oven.