Yes, you can. I prefer to make it fresh because it only takes a few minutes, but if you wanted to meal prep and make a large quantity at once, you can certainly freeze individualize-size portions. To reheat, you can certainly use a low setting on the microwave, but I prefer to let it thaw in the fridge overnight and then warm it in a skillet. This way I can add more heavy cream if needed and heat it gently enough that the gravy doesn't split.