Bring a pot of water to a boil and, one at a time, blanch the tomatoes for 4–5 seconds. Transfer the tomatoes to a bowl of cold water. Slice them in half and peel off the skins. Coarsely chop the tomatoes and set aside.
Heat the olive oil in a heavy-duty skillet, then sauté the garlic and onion over medium heat until the vegetables are fragrant and translucent. Add the chopped tomatoes