Sweet Potato Soup Base

Name: Sweet Potato Soup Base
Ingredients: 2 (10- to 12-ounce) sweet potatoes; 2 tablespoons extra virgin olive oil; 2 carrots, peeled and thinly sliced; 1 celery stalk, thinly sliced; 1 small leek, white and pale greens, thinly sliced; 2 sprigs thyme; Kosher or sea salt; Pinch of curry powder; 2 cups light chicken or vegetable stock, warmed