1Using a food processor fitted with a blade attachment, pulse the tomatoes and their juices, in batches as needed, until coarsely chopped (about 10 pulses). Heat the oil in a large saucepan with a tightfitting lid over medium-high heat until shimmering. Add the onion and cook, stirring occasionally, until translucent, about 3 minutes. Add the garlic and cook until fragrant, about 30 seconds more.
2Push the onions and garlic to one side of the pan and add the tomato paste to the empty side of the pan. Cook the paste slightly to remove the raw flavor, stirring occasionally, about 1 to 2 minutes. Stir the onions and garlic into the paste to incorporate. Add the chopped tomatoes, bay leaf, red pepper flakes, and a few pinches of salt. Bring the mixture to a boil, then reduce the heat to low, cover, and simmer for 45 minutes to meld the flavors.
3Add the capers, taste, and season with additional salt and red pepper flakes as needed.