From: Mark Bittman
3 dozen littleneck clams (3 pounds or more), or an equivalent amount of other clams
1 medium onion, peeled and minced
2 large potatoes (about 1 pound), peeled and cut into 1/4-inch dice
Salt and freshly ground black pepper
1. Wash clams well, scrubbing if necessary to remove external grit. Place them in a pot with half-cup water, and turn heat to high. Steam, shaking pot occasionally, until most of the clams are open, 7 to 10 minutes. Use a slotted spoon to remove clams to a broad bowl; reserve cooking liquid.
2. When clams are cool enough to handle, shuck them over the bowl, catching every drop of their liquid; discard shells. If any clams remain closed, use a thin-bladed knife to pry them open (it will be easy).
3. Chop clams. Strain all liquid through a sieve lined with a paper towel or a couple of layers of cheesecloth. Measure liquid, and add enough water to make 3 1/2 cups.
4. Combine liquid with onion and potato in saucepan; cover, and bring to a boil. Reduce to a simmer, keep covered, and cook until potatoes are tender, about 10 minutes. Stir in the clams, season with salt and pepper to taste, and serve.
New England Clam Chowder: add 1/2 cup or more of milk, cream or half-and-half along with the chopped clams.
Manhattan Clam Chowder: add 1 cup peeled, seeded and diced tomatoes (canned are fine) to the steaming water.
Rhode Island Clam Chowder: replace potatoes with 1/2 cup minced celery.
Steam clams in white wine instead of water.
Add 3 cloves of crushed garlic to the steaming water; discard them with the shells.
Garnish chowder with minced parsley or other herbs.