You can! You've got a couple of options. First, you can make the whole dish up to a few days in advance and gently reheat it in the microwave, oven, or on the stovetop just before serving. Or you can braise the kale and caramelize the onions in advance and finish the dish in about five minutes before serving. It's up to you — both methods work beautifully. Leftovers will keep in an airtight container in the fridge for three to four days.