2 medium sweet potatoes peeled and cut into 1/2 inch dices
2 tablespoons corn oil
salt and freshly ground pepper
1 pound frozen (rinsed and defrosted) or fresh corn kernels (about 4 cups)
1 cup water
1 1/2 cup finely diced celery
1 cup diced red onion
1/4 cup diced shallots
1 tablespoon tomato paste
1/2 teaspoon dried thyme leaves
3 cups vegetable broth
1 bay leaf
1 russet potato
2 tablespoons minced parsley
Set the oven rack in the center and preheat the over 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, 15-20 minutes.
Reserve 1 cup of corn kernels. In a blender, puree 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 TB 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, pureed corn, bay leaf, 1 teaspoon salt, and pepper to taste.
While bringing the chowder to a boil, peel the potato, cut it inch ½ 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. Adjust seasonings.