1/4 cup margarine
3 cups ketchup
1/2 teaspoon salt
1/3 cup brown mustard
1 cup milk
Boil the margarine and ketchup in a large saucepan. Remove from heat; pour into a blender or food processor or using a knife, and puree. Add mustard, milk, and blend until well mixed.
Carefully remove the edges of the crust from the container and place inside the refrigerator.
Bake at 350 degrees F (175 degrees C) for 20 to 25 minutes in the Preheated 350 degrees F (175 degrees C) oven.
Let cool in pan for 10 minutes; remove from pan. Cool completely.