Coat a medium sauce pan with cooking sprat. Add onion and celery, and cookuntil tender. Gradually sprinkle flour over mixture and stir until flouris browned, about 2-3 minutes. Stir in broth and evaporated skim milk.
Bring to a boil, reduce heat and simmer until thickened. For bestconsistency, strain through cheesecloth or a sieve. Season to taste withsalt and pepper.