This is one of those subjects I could give a two hour talk on off the top of my head. I’d probably run over time. I’ll keep this brief for the time being, sticking to the subject of White Clam Chowder and leaving aside other varieties of clam chowder, and chowders containing other meats besides or in addition to clams.
White Chowder (or simply White) is the proper designation for what is often called New England Clam Chowder. It’s necessary ingredients are clams and ‘white’. The ‘white’ being milk and/or cream. The clams may be any variety but mostly are chopped Cherrystones or Quahogs. Smaller clams of the Littleneck variety may used, as well as razor clams or soft shell clams. For chowder clams is not only the meat but plenty of clam juice also. After that the subject becomes complicated because people are very picky about what goes into their chowder. The most common additions are potatoes, onions, and thickeners. There is some set of people that also add salt pork of some variety, usually considered a tasty addition to any dish but likely to set off some chowder purists into a frenzied rage.
The simplest chowder may be nothing but milk and clams. Any kind of clams, chopped or whole, and slowly simmered to infuse the flavor of the clams into the liquid. My thin white chowder would use this method, coarsely chopped clams, lightly browned onion strings, and milk or cream. For almost all white chowders I use about a 2:1 ‘white’ to clam juice ratio.
From that same base, either with or without the onions I can add diced potatoes. I use firm Russets for this so the potatoes don’t just turn to mush.
When thickening chowder a white flour and butter and roux is best. However if you want eat it with a fork consistency you need to start with cream or add plenty of butter to avoid a starchy taste. Another approach if you don’t mind it being a little starchy and ‘grainy’ is to add crumbled saltines or oyster crackers to the chowder. They’ll absorb liquid as the chowder simmers but the chowder won’t have a consistently creamy appearance. Most people don’t care, they like the way the crumbs carry the flavor.
White chowder is best heated in a double boiler, slowly, well below the boiling point to avoid any burning and leaving lots of delicious bits of clam stuck to the bottom of the pot.
For clams use what you can find. If you get whole clams steam then in a pot with just half an inch of water until they open, let them cool down until you can handle them, then scoop out the meat with a spoon or your fingers. Use a spoon/and or knife to scrape out the necks and any bits stuck to the shell. If you use soft shell clams (called ‘steamers’ here in Ningland) remove any of the black membrane around the clam and on the neck (the part you hold to eat them). Do this over a bowl to catch all the clam juice. If the clams have full bellies you can rinse them if you like but it’s all delicious flavor. If the water from the steaming is clean you can use that for clam juice also.
You can buy chopped clams and maybe chopped quahogs in these parts. They’re usually from large clams and not as flavorful as the smaller ones but still perfectly fine. Ask the seafood vendor to drain the juice before weighing the chopped clams, then ask them to add more, which they will usually do. You can also use canned clams. Not as exquisite in flavor but still plenty clammy. And you can buy bottled and canned clam juice as well as clam base.
For proportions in a basic thick white chowder use 2 pounds of chopped clams, 1 pint of heavy cream, and 1 cup of clam juice. Use about 1 pint of diced potatoes. Melt 4 tablespoons of butter in a pot and stir in two heaping tablespoons of white flour. Slowly stir in the cream then add the clams and potatoes. Bring the mix to nearly a boil while stirring so the flour will thicken properly, then lower the heat and keep covered at a very low simmer until the potatoes are tender.
I almost always add some coarse ground black pepper and a dash of celery salt but it’s just a matter of taste.