Heat a large pot over medium-low heat and add 1 tablespoon olive oil. Add onions and stir. Cook 20 to 30 minutes until onions begin to soften and turn golden.
Stir in sugar. Cook until onions are very soft and brown, about 30 additional minutes.
Preheat oven to 400 F.
While the onions cook, spread cut halves of tomatoes with remaining olive oil and place in a roasting pan. Roast tomatoes until skins blister, about 25 minutes. Cool until easy to handle then remove peel and seeds and coarsely chop. Don’t discard juices in pan.
When the onions are caramelized, turn heat to medium and add garlic. Saute 1 minute.
Stir in wine, tomatoes, reserved tomato juices, tomato paste and thyme. Raise heat and bring to a boil. Lower heat and simmer for 5 minutes until liquid reduces by a third.
Stir rice into pot and allow mixture to simmer until most of the remaining liquid is absorbed, stirring frequently.
Begin adding heated broth about 1 ladle at a time, allowing the rice to absorb the liquid before adding the next one. Continue process until rice has absorbed 3 to 4 cups and is tender. This process takes around 20 minutes.
Stir in Parmesan, butter, salt and pepper until creamy. Serve.