Rich, chewy cookies with nutty brown butter, bold espresso flavor, and crunchy toffee bits throughout. Perfect for coffee lovers and cookie enthusiasts.
Preheat oven to 375°F (190°C) and line baking sheets with parchment paper.
Melt butter in a light-colored saucepan over medium heat. Continue cooking, swirling occasionally, until butter foams and turns golden brown with nutty aroma, about 5-7 minutes. Pour into heatproof bowl and cool for 10 minutes until it reaches 90-100°F.
Combine cooled brown butter with both sugars in large bowl. Beat with electric mixer for 2-3 minutes until creamy. Add eggs one at a time, beating well after each. Mix in vanilla extract and espresso powder.
In separate bowl, whisk together flour, baking soda, cornstarch, and salt. Gradually add to wet ingredients, mixing on low until just combined.
Fold in toffee bits using spatula until evenly distributed throughout dough.
Drop rounded tablespoons of dough onto prepared baking sheets, spacing 2 inches apart.
Bake for 10-12 minutes until edges are golden brown and centers appear just set but still soft. Let cool on baking sheet for 5 minutes.
Transfer cookies to wire rack to cool completely before serving or storing.
Notes
Use light-colored saucepan for browning butter so you can see color changes clearly. Stop when you see golden specks and smell nutty aroma to avoid bitter flavor.
For thicker cookies, chill dough for 30 minutes before baking. Cookies can be frozen (baked or as dough) for up to 3 months.
Room temperature eggs incorporate better into brown butter mixture. Let butter cool to 90-100°F before adding to prevent scrambling eggs.