Chicken, Cheese and Green Chilies Soup

6 cups chicken stock
2 10 oz cans Ro-tel tomatoes w/green chilies
2 tablespoons butter or margarine
2 tablespoons vegetable oil
1 large onion, diced
1 4 oz can diced green chilies
2 teaspoons ground cumin
2 teaspoon chili powder
1/2 cup flour
2 cups milk (skim, whole or 1/2&1/2)
12 oz sharp cheddar cheese, grated
1/2 cup drained plain yogurt
2 cups chopped cooked chicken
salt & pepper to taste
tortilla chips

In large soup pot, bring stock to boil.
Add tomatoes.
Lower heat, cover and simmer.

In large skillet, heat butter and oil.
Add onion and sauté until onion is translucent (about 4 minutes).
Add green chilies.
After 2-3 minutes add cumin and chili powder.
Stir.
Sprinkle in flour, blending in with a spoon.
Gradually add milk, stirring until smooth.
Cook until thickened.
Add 1 cup stock to milk mixture and stir.
Pour contents of skillet into soup pot.
Let it cook at bare simmer — very low heat — stirring often, 15 minutes.

Very slowly stir in grated cheese and strained yogurt.
Cook 5 minutes more, stirring often.
Add chicken.
Salt and Pepper to taste.
Add Tabasco if desired.
Serve hot with chips.