Beat both sugars and butter together in a medium bowl with an electric mixer until creamy and fluffy. The color will have changed to a paler beige.
Add the egg, miso, and vanilla and beat until it’s well mixed.
In a separate bowl, whisk together flour, cornstarch, and baking soda. Add this dry mixture to the dough and mix with a spatula or wooden spoon (not beater!!) until just combined. Lastly, mix in your chocolate chips.
Cover the bowl with plastic wrap and refrigerate for at least an hour or freeze until you’re ready to bake! Don’t even attempt to bake this until you’ve done one of those two steps. >:-(
Preheat your oven or toaster oven to 350 degrees F and prepare a baking sheet with parchment paper or aluminum foil.
If your dough was frozen, let it sit in the fridge for an hour or on the counter for 30 minutes. If it was refrigerated, we can get to scooping right away!
Form 1-2 inch dough spheres with an ice cream scoop and place them on your prepared sheet, about 1.5 inches apart from one another.
Chop up your bar of bittersweet chocolate into shards and chunks and plop a few onto the tops of each cookie sphere. These will form yummy pools of chocolate later.
Place the cookies in the oven and set a timer for 10 minutes. At the end of the timer, your cookies should be a bit puffy with golden brown tops and edges. Turn the temperature down to 325 and return the sheet to the oven, rotating it once. Set a timer for 3-4 minutes, but keep an eye on them. Some ovens are stronger than others and may finish baking the cookies faster. This second bake in the oven will prevent raw interiors while maintaining your cookie’s thicker figures.
Remove your cookies from the oven and let them rest for at least 15 minutes before removing off the sheet (with a flat spatula).
Feed this cookie to people without telling them it’s filled with miso, then tell them after they take a bite. The reaction is priceless.