In a small saucepan over medium heat, melt the butter. Once melted, use a heatproof silicone spatula to frequently stir and unstick any brown bits from the bottom and sides of the pan. Cook until the butter turns deep amber in color and emits a nutty aroma.

Immediately transfer the browned butter to a large heatproof bowl. Be sure to scrape out every last bit of browned milk solids as that's where the majority of the flavor is. Cool at room temperature for 20 minutes.

In a medium bowl, whisk together the flour, baking soda, and salt. Line a small baking sheet with parchment paper and set aside.

Add both sugars to the lightly cooled butter and whisk until well combined and slushy.

Add the miso, egg, and vanilla extract and whisk until smooth.

Fold in the flour mixture until just combined then fold in the dark chocolate.

Use a 3 tbsp cookie scoop to portion out the cookies and place them side by side on the small lined baking sheet. Chill in the fridge for at least 1 hour or overnight for best results.

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

Place the cookies 2-3 inches (5-7.6 cm) apart on the prepared baking sheet. Bake for 12-14 minutes or until the edges are golden brown and the centers look slightly underdone.

Cool on the pan for 5 minutes then transfer to a wire rack to continue cooling.