01 - Place butter in a medium saucepan over medium heat. Melt and cook, stirring frequently, until the butter foams and develops brown specks and a nutty aroma (about 4–5 minutes). Remove from heat and let cool for 10 minutes.
02 - Pour browned butter into a large mixing bowl. Add both sugars and whisk until well combined.
03 - Add eggs, one at a time, mixing well after each. Stir in vanilla extract and milk.
04 - In a separate bowl, whisk together flour, baking soda, baking powder, salt, and espresso powder.
05 - Gradually add the dry ingredients to the wet ingredients, mixing just until combined.
06 - Fold in chocolate chips and toffee bits.
07 - Cover dough and chill for at least 30 minutes (up to 24 hours for more flavor).
08 - Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
09 - Scoop heaping tablespoons of dough onto baking sheets, spacing 2 inches apart.
10 - Bake for 11–13 minutes, or until the edges are golden and centers are just set.
11 - Cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.