Blanch tomatoes in 3 batches in a pot of boiling water for 10 seconds per batch.
Transfer with a slotted spoon to a bowl of cold water.
Peel, seed, and finely chop tomatoes.
Heat oil in a deep 12 - 13 inch heavy skillet over medium heat until hot but not smoking, then saute onion (without browning), stirring, 3 minutes.
Add garlic and saute, stirring, until garlic and onion are pale golden, about 1 minute.
Stir in tomatoes, sugar, salt and bay leaves and bring to a boil.
Reduce heat to medium-low and simmer, uncovered, stirring occasionally, until most of the liquid is evaporated, 20 to 30 minutes.
While the sauce cooks, pre-heat oven to 200 F.
Add olives, raisins, capers, and oregano to sauce and cook, stirring, 1 minute. Transfer sauce to a baking dish, discarding bay leaves, and keep warm, covered, in the oven.