Have all your ingredients prepped, weighed, and ready.
Add the bacon, shallots, and garlic into a large, pan and cook over moderate heat until the onions and garlic have softened, and the bacon has cooked through safely.
Add the balsamic vinegar to the pan and mix well. It will disappear (evaporate) quickly, but it does a great job of deglazing the pan while adding a little acidity to the dish.
Increase the heat to high and add all the Brussels sprouts, stirring continuously until they soften, approx. 2-3 minutes.
Season with black pepper and more balsamic if desired (and salt, only if needed).