To reheat mac and cheese, transfer it to a saucepan or microwave-safe bowl. Add 1 to 2 tablespoons of milk and stir. Place the saucepan on a stove top over medium-low heat and stir until consistency is smooth and noodles are warmed through. If microwaving, heat in 1-minute bursts, stirring after each, until cheese has melted and the noodles are heated through.