To reheat the vegan cheese sauce alone, either microwave in 1 minute bursts, stirring between each or add it to a small saucepan over low heat and stir until the sauce is smooth and creamy. To reheat any leftover mac and cheese, you can again do this on the stove in a small saucepan or in the microwave, just add a splash of extra plant based milk to help loosen up the sauce and ensure it gets creamy again as you stir.