Brown the butter:
In a saucepan over medium heat, melt the butter. Continue cooking until it turns golden brown and releases a nutty aroma. Let it cool for about 10 minutes.
Combine wet ingredients:
In a large bowl, whisk together browned butter, brown sugar, and granulated sugar until smooth. Add the eggs and vanilla; mix until creamy.
Mix dry ingredients:
In a separate bowl, whisk together flour, baking soda, baking powder, salt, and espresso powder.
Form the dough:
Gradually stir dry ingredients into the wet mixture. Fold in the toffee bits and chocolate chunks.
Chill:
Cover and refrigerate dough for at least 30 minutes to prevent spreading and deepen the flavor.
Bake:
Preheat oven to 350°F (175°C). Scoop tablespoon-sized balls of dough onto parchment-lined baking trays. Bake for 10–12 minutes until edges are golden and centers are slightly soft.
Cool:
Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack.