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Melt margarine in a large saucepan (1 1/2 or 2 quarts / litres). Blend in the flour and salt.
Heat until 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 the milk. Heat rapidly, without boiling. Serve hot.
Makes 1 quart.
posted by T5NF