Preheat oven to 450°F. Line baking tray with foil if desired.
Clean Brussels sprouts, trim the bottom, and remove any spoiled leaves. Cut sprouts in half lengthwise.
In a large bowl, combine sprouts (along with any stray leaves) with olive oil, 1 tablespoon balsamic vinegar, and syrup if using. Season with salt and pepper.
Place sprouts flat side down. Roast 18-22 minutes, and check after 15 minutes. Keep the cut side down so it becomes nicely browned.
Drizzle with remaining balsamic and season to taste before serving.
Notes
The sprouts will roast to a dark brown color, and may brown even more when using the syrup or honey. Make sure to remove before they burn or blacken.
Refrigerate leftovers in a covered container for up to 4 days. Or freeze them in a zippered bag up to 4 months.
Reheat Brussels under the broiler with fresh balsamic, or reheat for 30-second intervals in the microwave.