Preheat oven to 300°.
Coarsely chop tomatoes with juice in a food processor.
Put roast in an ovenproof 4- to 5-quart heavy pot or a casserole dish with a lid.
Pour tomatoes over roast and scatter garlic around it.
Season with salt and pepper.
Braise in middle of oven, covered, until very tender, 3 to 4 hours.
Cut roast into ¼-inch-thick slices and serve with sauce and garlic.
