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Melt margarine in a large saucepan (1 1/2 or 2 quarts / litres). Blend in the flour and salt, and heat until the mixture bubbles. Remove from heat and gradually stir in hot tomato mixture. Return to heat and bring to boiling, stirring constantly; cook 1 to 2 minutes long. Slowly stir hot tomato mixture into milk.
Heat rapidly, without boiling. Serve hot.
Makes 1 quart.
posted by Fritz/T5NF