Melt 2 sticks of unsalted butter in a medium sauté pan over medium heat, swirling occasionally until it turns golden brown and has a nutty aroma.

Mix ½ cup of granulated sugar and 1 cup of dark brown sugar into the cooled browned butter until smooth and creamy.

Whisk together 1 ½ cups of all-purpose flour, ½ cup of bread flour, 1 teaspoon of baking soda, ½ teaspoon of baking powder, ½ teaspoon of fine sea salt, and 1 teaspoon of instant espresso powder in a separate bowl.

Add 1 large egg, 1 egg yolk, and 2 teaspoons of vanilla extract to the butter-sugar mixture, stirring until fully combined.

Fold the dry ingredients into the wet mixture gradually, then gently fold in 1 cup of chopped semisweet chocolate and 1 cup of toffee bits.

Wrap the dough in plastic wrap, form into a disc, and refrigerate for a minimum of 24 hours.

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

Portion out the chilled dough using a 3-tablespoon-sized cookie scoop onto the baking sheets, leaving 2 inches of space between each ball.

Bake for 12 to 14 minutes until edges are golden brown and centers are set but still soft.

Sprinkle with flaky sea salt while warm and cool on wire racks before enjoying.