Pour milk into a microwave-safe container and heat in a microwave oven until warm, about 2 minutes.
Melt margarine in a saucepan over medium heat. Whisk in flour and continue cooking until the mixture bubbles, about 5 minutes. Pour milk into the saucepan slowly while whisking. Cook and whisk until the mixture begins to thicken, about 3 minutes. Add salt and pepper. Continue whisking until the gravy comes to a boil, about 3 minutes more. Remove from heat.
