Heat oil and water in a 5-qt. saucepan over low heat.
Add celery, carrots and onion.
Season with salt and pepper.

Saute onions until translucent, about 8-10 min.
Remove from heat and set aside at room temperature.
Bring chicken stock to a boil in a 2 1/2 qt. saucepan.
Melt butter in another 2 1/2 qt. saucepan over low heat.
Add flour to make a roux and cook, stirring,
until mixture bubbles, about 6-8 min. Stir
constantly to prevent browning and scorching.
Add boiling stock and whisk vigorously until smooth.
Bring to a boil, reduce heat and simmer for 15 minutes.
Remove soup from heat. Whisk in grated cheese,
1 cup at a time. Add sauteed vegetables, and salt
and pepper to taste. Serve immediately or hold up to
1 hour in top of double boiler. Makes 8 servings.