First, melt butter in a saucepan over high heat. Once melted lower the heat to low and cook until brown bits start to appear. Remove from the heat and set aside.
Combine all purpose flour, baking soda, and salt in a bowl. Mix and set aside.
Combine the browned butter, light brown sugar, dark brown sugar, and granulated sugar in a large bowl or the bowl of a stand mixer. Mix until combined.
Add the egg and vanilla extract. Whisk for 5-10 minutes until the mixture becomes light and creamy.
Add the white miso and mix until combined.
Add the dry ingredients from step 2. Mix until just combined. Don't over mix the batter.
Finally, add the dark chocolate and mix until just combined.
Let the dough rest in the fridge for at least 1 hour. This helps the prevent the butter from melting too quickly in the oven and helps improve the flavor and texture of the cookie.
Preheat the oven to 350 degrees F (177 degrees C). Move one oven rack to the top third and another one to the bottom third of the oven.
Prepare 2 baking sheets by covering them with parchment paper.
Use a 2 tablespoon (medium sized) cookie scoop to scoop your cookie dough onto the prepared baking sheet. Make sure there are 2 inches of space between each cookie.
Bake for 10-12 minutes until the edges are light brown. Halfway through the baking process, move the baking sheet on the bottom rack to the top rack and the one on the top rack to the bottom rack. This ensures even baking for all cookies. You can also bake each baking sheet separately in the center of the oven.
Rest for 10 minutes on the baking sheet and then another 10 minutes on the cooling rack before serving.