To keep this dish strictly keto, be sure to use sugar-free sauerkraut and sugar-free ketchup, and double-check the label on your corned beef for added sugars or starches. For meal prep, store the cooked corned beef and sauerkraut mixture separately from the dressing, then reheat the meat base and broil with cheese just before serving, adding the cold dressing afterward to keep it creamy. For extra volume without many carbs, you can serve the Reuben mixture over a bed of lightly sautéed shredded green cabbage or raw coleslaw mix tossed with a bit of olive oil, keeping total net carbs per serving under the keto limit.