1/4 cup finely chopped onion
1 cup finely chopped leek, washed well and drained
2 large garlic cloves, minced
3 large carrots, finely chopped
1 bay leaf
3 TBSP butter
2 lbs (about 3 large) sweet potatoes, peeled and cut into 1-inch cubes
1/2-pound russet (baking) potato, peeled and cut into 1-inch cubes
6 cups vegetable broth
sour cream for garnish
In a Dutch oven, melt butter over medium heat, and then add onion, leek, garlic, and carrots with the bay leaf and salt and pepper to taste. Cook until softened, about 3-5 minutes. Add the sweet potatoes, regular potatoes and broth. Simmer until the potatoes are tender, about 15-20 minutes. Discard the bay leaf. With a potato masher, puree the mixture until reasonably smooth. Divide the soup among bowls and top each serving with a dollop of sour cream.
If you wish, you may add a cup of white wine along with the broth. Also, you may puree the finished soup with an immersion blender or in a food processor before serving. I like it a little chunky myself so that is why I just use the potato masher.