Thought this looked easy and might taste pretty good. 
Potato Cream Soup
1 tbsp vegetable oil
2 cups diced sweet onion
2 cups diced sweet potato
1 cup diced white potato
4 cups reduced-fat chicken broth (or vegetable broth)
Salt and pepper
2 cups plain kefir
2 tbsp chopped chives
1. In a soup pot, heat oil. Add onion and sauté 3-4 minutes.
2. Add sweet and white potatoes and chicken broth; bring to a boil.
Then reduce heat and simmer 25-30 minutes.
3. Puree soup and season with salt and pepper.
Whisk in kefir and serve with a sprinkling of chives.
Yield: 6 servings. Analysis per serving: 171 calories, 5.5g protein,
5.5g fat, 25g carbohydrates
Source: Lifeway Foods (www.lifeway.net)