Preheat oven to 275°F.  

Arrange tomatoes on a sheet pan, cut sides up, in a single layer.  Drizzle with the olive oil and balsamic vinegar.  (If you prefer, oil and vinegar can be mixed in a small bowl, then applied with a basting brush.)

Evenly sprinkle the tomatoes with the garlic, sugar, salt and pepper.  Roast for 2 hours until the tomatoes are concentrated and begin to caramelize.  If the tomatoes are on the large side, they may need to roast longer.

Allow the tomatoes to cool at room temperature.  If not using right away, store in an closed container in the refrigerator for up to a week.