Clam chowder is a thick soup typically made of clams, diced potatoes, onion and bacon. There are three different varieties of clam chowder: Manhattan clam chowder, which has a tomato base; Rhode Island clam chowder, which has a clear base; and New England clam chowder, which has a cream base. This clam chowder Instant Pot recipe is a spin on the New England version and is made way easier in the pressure cooker.