Brown the butter by melting 1 cup of unsalted butter over medium heat in a sauté pan, stirring occasionally until golden brown.

Combine ¾ cup granulated sugar and ¾ cup dark brown sugar in a mixing bowl, add the cooled browned butter and mix until well combined.

Prepare dry ingredients: whisk together 2 cups all-purpose flour, ½ cup bread flour, 1 teaspoon baking soda, ½ teaspoon baking powder, 1 teaspoon fine sea salt, and 1 teaspoon instant espresso powder.

Mix in wet ingredients by whisking in 2 large eggs and 2 teaspoons vanilla extract, then gradually add the dry mixture until just combined.

Fold in 1 ½ cups chopped semisweet chocolate and 1 cup toffee bits into the dough using a spatula.

Chill the dough wrapped in plastic wrap in the refrigerator for 24 to 72 hours to enhance flavor.

Preheat oven to 350°F (175°C) and line baking sheets with parchment paper, scoop 3-tablespoon sized balls of dough onto sheets.

Bake cookies for 12 to 14 minutes until golden brown around edges but soft in center, reshape if necessary.

Sprinkle flaky sea salt on warm cookies and cool on baking sheets for 5 minutes before transferring to wire racks.