Preheat the oven to 400ºF. Prepare a baking sheet: line a baking sheet with parchment paper OR foil sprayed with nonstick cooking spray. You can also spray the baking sheet directly. Set aside.
Prepare the Brussels sprouts: Scrub the Brussels sprouts under warm water to remove any dirt. Pat dry with a towel. Use a sharp knife to cut both ends off of each Brussels sprout. If some of the leaves fall off, don't worry! You'll roast these, too. Then, cut them in half longways (hot-dog style). The goal is to get all of the Brussels sprouts around the same size so that they roast evenly. If you have some extra-large sprouts, you may need to quarter them. Transfer the halved Brussels sprouts to the prepared baking sheet.
Drizzle the Brussels sprouts with a generous amount of olive oil and the balsamic vinegar. Add the minced garlic. Use your hands to massage the oil and vinegar into the sprouts.
Evenly spread the Brussels sprouts out onto the baking sheet. Make sure they don't touch – if they overlap at all, they will not roast evenly.
Bake for 25-30 minutes, tossing the Brussels sprouts every 10 minutes. Brussels sprouts are done when they're brown and crispy.
Before serving, sprinkle the balsamic Brussels sprouts with sea salt and enjoy.