How to Make It
Cook chopped shallots and chopped garlic in a large skillet coated with cooking spray over medium-high until softened, about 2 minutes. Add sliced shiitake mushrooms; cook until browned, 5 minutes. Add unsalted chicken stock, white wine, and balsamic vinegar; bring to a boil. Reduce heat to medium; cook until reduced by half. Stir in unsalted butter, kosher salt, and black pepper.