Oyster House on Sansom Street and order the lobster roll. It’s a bit pricey, but it’s worth every penny. There’s a full five ounces of meat tucked into the top-split roll (about the same amount you’d get from a 1-1¼-lb. live lobster), and it’s in huge chunks that beg you to pluck them right off the top.
You can get away with snatching a few with your fingers, because the lobster isn’t weighed down by a heavy dressing - it’s done true New England style, very light and slightly lemony, with just a few pieces of celery and a sprinkling of scallions.
The buttery grilled bun is just about all else you need, although you do get a hefty helping of Old Bay seasoned chips on the side. The sandwich is so filling, though, you probably won’t have room for them ($26; 215-567-7683).