In a saucepan over medium heat, melt the butter. Cook, stirring frequently, until the butter foams and the milk solids turn golden brown and smell nutty (*see notes). Pour into a large mixing bowl and immediately stir in the milk powder(**see notes) and espresso powder if using. Let the brown butter sit for at least 20 minutes. It will be cool enough to touch.

Preheat oven to 350°F (175°C) and lightly grease an 8-inch pan.

Add the brown sugar and granulated sugar to the cooled brown butter. Whisk for 1 minute until the mixture becomes smooth and glossy.

Whisk in the whole egg, and vanilla extract or vanilla bean paste until fully combined.

Add the flour, cornstarch, baking soda, and salt. Fold until a soft dough forms with some flour streaks remain. Add chopped chocolate‍.

Scoop large portions of dough about a 1/4 cup of dough per cookie and place in a 8-inch lightly greased pan and backed at ‍350°F (175°C) for 20 minutes until edges are golden but center is soft.

Sprinkle flaky salt and let scoopable cookies set in the pan for at least 10 minutes to set. Serve warm with vanilla ice cream.