Beat the eggs and sugars in a stand mixer fitted with the whisk attachment until pale in color and fluffy, about 4 minutes.
2 large eggs, room temperature, 3/4 cups powdered sugar, 1/2 cup granulated sugar
Meanwhile, melt the chocolate bar pieces and butter in the microwave in 30-second increments until smooth and melty. Whisk in the oil, vanilla, and balsamic. It will be smooth and a little thick.
8 oz. semi-sweet chocolate bars (I used 2, 4 oz. Ghirardelli Bars) , 4 Tbsp. unsalted butter, 1 Tbsp. canola or vegetable oil, 1 tsp. vanilla, 1 tsp. balsamic vinegar
Stir the melted chocolate mixture into the egg/sugar mixture. (Pretty swirls!)
Whisk together the dry ingredients.
1/2 cup all-purpose flour, spooned and leveled, 1/2 cup dutch process cocoa powder, 1 tsp. cornstarch, 1 tsp. espresso powder, 1 tsp. salt
Fold dry ingredients into the wet ingredients. Do not over mix.
Chill at least 1 hour in the fridge or longer/overnight in the fridge if needed.
When ready to bake, preheat the oven to 350°F. Line 2 baking sheets with parchment paper or silicone baking mats.
Allow the cold cookie dough to rest on the counter for a few minutes to make it easier to scoop. It's really chocolatle-y and fudgy but you will still be able to roll the dough together in the palms of your hands.
Roll the cookies first in granulated sugar, then roll HEAVILY in the powdered sugar. A really good coating of powdered sugar = cookies stay bright white.
1/4 cup granulated sugar, 1/2 cup powdered sugar, or more as needed
Place cookies on the prepared baking sheet. Bake for just about 8-10 minutes, better to underbake them slightly. Swirl a cup around the cookies when they come out of the oven while they’re still warm to make them perfect circles, if needed.
Cool on cookie sheet for just a few minutes, then carefuly transfer to wire rack to cool completely. ENJOY!