New England Clam Chowder

The worst thing about commercial chowders is how glutinous they are. The second worst thing is the predominance of potatoes over clams. Fortunately, you can rectify both problems by making the chowder yourself. Any type of hard-shell clam will do, but I use the large ones, sold as "quahogs," because they're by far the cheapest. What's most important is that the clams are fresh.

(serves eight)

8 lb fresh hard-shell clams (about 20 quahogs)
¼ lb pancetta (or bacon)
2 large onions
2 lb potatoes
2 Tbs ...