Asparagus & Cheese Potato Soup

1 large onion, chopped
4 teaspoons of canola oil
3 tablespoons all-purpose flour
1½ cups 1-inch pieces asparagus spears or broccoli florets
2 cups of lowfat Milk
1 14-ounce can reduced-sodium chicken broth
1½ cups ½-inch cubes red potatoes
1½ cups ½-inch cubes gold potatoes
¼ teaspoon salt
1⁄8 teaspoon cayenne pepper
¾ cup shredded sharp cheddar cheese
1⁄3 cup sour cream

In a large saucepan cook onion with oil until tender. Sprinkle flour over onion and stir. Add the asparagus, milk, broth, potatoes, salt and cayenne pepper.
Cook and stir until the soup has thickened; reduce heat. Simmer and cover for about 10-12 minutes or until the vegetables are tender. Add cheese and sour cream; stir until cheese melts. Then it is ready to serve.