Preheat the oven to 375 degrees F. Trim/clean the Brussels sprouts, then cut them in half. Arrange on 2 baking sheets and toss with the olive oil. Roast until brown, 25 to 30 minutes. Combine the balsamic vinegar and sugar in a saucepan. Bring to a boil, then reduce the heat to medium-low and reduce until very thick. Drizzle the balsamic reduction over the roasted sprouts, then sprinkle on the dried cranberries.
