Brown the butter. Brown butter in a saucepan on medium heat, swirl the butter around the saucepan, until butter foams and starts to turn brown and has a nutty aroma. As soon as the butter starts to have some brown bits and smell nutty, take it off the heat to prevent any more liquid from escaping. Transfer butter to a liquid measuring cup and see how much water content you lost. You want to have ½ cup of butter, so stir in 1 tablespoon of butter if you need it. Set aside to cool.

Mix wet ingredients. When the butter is melted and slightly cool, in a large mixing bowl, whisk the butter with the brown and white sugars until incorporated with no lumps remain. Add in the egg, miso, and vanilla until smooth and glossy.

Whisk the remaining dry ingredients. Whisk together the flour, baking soda, and salt in a separate mixing bowl. Using a rubber spatula, fold in half the dry ingredients into wet ingredients until everything comes together. Slowly add in the remaining flour and mix until combined. Fold in the chocolate.

Scoop then chill the cookie dough. Use a 1 oz cookie scoop and scoop out into balls placing them parchment paper, or slipmat lined baking sheet. Cover with plastic wrap and refrigerate the cookie dough for at least 30 minutes or up to 24 hours.

Preheat the oven to 350°F. Bake the dough 2 inches apart until golden brown and firm around the edges, 10-11 minutes, or until the edges are just golden brown and the center is puffed up and gooey. (For a more flattened cookie, lightly tap the tray on the counter when you remove it from the oven.) Sprinkle with flaky sea salt, cool on the baking sheets, and enjoy!