In a microwaveable bowl, melt the chopped chocolate and butter together for 20 second increments. (I like to turn the power down to 50% to avoid burning). Stir in-between increments until the melted chocolate looks smooth.
4 oz bittersweet chocolate, 3 tbsp unsalted butter
In a stand mixer fitted with the whisk attachment, add the egg and both sugars. Mix on high speed for 3-4 minutes until light in color and looks like it has doubled in size. The extra whipping will help the cookies to slightly rise so don't skip this!
¼ cup light or dark brown sugar, ¼ cup granulated sugar, 1 egg
Turn the mixer on low, and slowly add the melted chocolate mixture and vanilla extract. Mix until incorporated.
½ tsp vanilla extract
While on low speed, slowly add the dry ingredients. Stop the mixture once there are no more streaks of flour.
To get those crackly brownie tops, don't let the dough sit! Scoop the dough onto the prepared baking tray about 2-inches apart, and bake asap. Bake for 9-10 minutes. Look for set edges, and a gooey middle.
Transfer to a wire cooling rack. Enjoy!
Notes
There is no chilling required. This cookie is fudgy and chewy in the center. To achieve this, make sure to bake the cookies ASAP after mixing!