Melt the butter in a medium saucepan over medium heat, then let it cook further for around 3-4 minutes, stirring occasionally until the milk solids have caramelized and the butter smells nutty. Pour it into a bowl and cool down for 10 minutes.

Add the sugar, espresso powder, vanilla, and egg to the butter and beat it until well combined. Don't worry if the espresso powder doesn't dissolve completely.

Mix the flour, baking powder, baking soda, and salt in a separate medium bowl. Stir the flour mixture into the cookie dough mixture until a dough forms, then add the chocolate chips. Continue stirring until it's all combined. If the cookie dough is still very warm due to the butter, let it cool a bit more before adding the chocolate chips so they don't melt into the dough.

Preheat the oven to 350°F (180°C) and line baking trays with parchment paper.

Roll the cookie dough into balls using around 2 tablespoons of dough for each or a medium cookie scoop. If the dough feels greasy, let it stand for 5 minutes, and it will firm up. Optional: Place the dough balls in the refrigerator for 20 minutes for thicker cookies.

Space them at least 2 inches apart on the cookie sheets.

Bake the cookies for 10-11 minutes until they have puffed and the edges have cooked. The cookies will still be very soft but will continue cooking on the hot oven tray once out of the oven and will firm up as they cool down. 

While the cookies are still hot from the oven, sprinkle them with flaky salt.