This cheery chowder has a satisfying, long-cooked taste. Roasting the sweet potatoes intensifies their flavor, and puréeing most of the corn kernels instantly creates a creamy broth. I've had excellent results using frozen organic corn. To streamline cooking, begin preparing the soup while the sweet potatoes are roasting. If the chowder becomes too thick, stir in soymilk to thin it while adding richness and flavor.
2 medium sweet potatoes (about 1 pound), peeled and cut into 1/2-in dice
2 tablespoons corn oil salt
freshly ground pepper
1 pound frozen (rinsed and defrosted) corn kernels or 4 cups fresh corn kernels
1 cup water
1 1/2 cups finely diced celery
1 cup diced red onion
1/4 cup diced shallots
1 tablespoon tomato paste
1/2 tablespoon dried thyme
3 cups vegetable broth
1 bay leaf
1 russet (baking) potato (about 8 ounces)
2 tablespoons minced parsley
1/2 to 1 cup unflavored soymilk (optional)
Set the oven rack in the center and preheat the oven to 425°F. Oil a large roasting pan.
Scatter the sweet potatoes in one layer in the roasting pan and drizzle with 1 tablespoon of the oil. Season well with salt and pepper. Roast until tender, tossing once or twice, 15 to 20 minutes. If you'd like to brown the sweet potatoes more deeply, set them about 5 inches below the broiling element for a minute or two. Set aside.
Reserve 1 cup of corn kernels. In a blender, purée the remaining corn with the water until very smooth, about 2 minutes. (If the corn kernel skins refuse to break down, and they look unsightly to you, pass the mixture through a sieve.) Set aside.
In a heavy soup pot, heat the remaining tablespoon of oil. Cook the celery, onion, and shallots over medium-high heat, stirring frequently, until the onions are slightly softened, about 3 minutes. Add the tomato paste and thyme and cook another minute, stirring frequently. Add the broth, puréed corn, bay leaf, 1 teaspoon salt, and pepper to taste.
While bringing the chowder to a boil, peel the potato, cut it into 1/2-inch dice, and add it to the pot. Cover the pot and simmer until the potato is tender, 25 to 35 minutes.
Remove the bay leaf. Add the reserved corn kernels, roasted sweet potatoes, and parsley. Thin with soymilk, if necessary. Adjust seasonings. Cook (but do not boil after adding soymilk) until heated throughout.