I am one of those people who’d never entertain the idea of replacing carbs with vegetables å la zoodles or cauliflower rice, but once this dish was born, I realized I was essentially using cauliflower as a replacement for pasta in this pasta-less version of what reminds me of macaroni and cheese. Believe me, I, too, was horrified, but it was so good that I did not and could not care.
This gratin is the easiest and most delicious way to make superlatively tender, creamy, cheesy cauliflower without any additional steps (no bechamel, roux, or other fancy sauce required). Bake the cauliflower, covered, in the cream, just to cook it through and get it tender, then uncover it so the cream can reduce, becoming thick and rich, and the cheese can get all browned and crispy.
It may seem like a crazy thing to do, but I left the bread crumbs optional for two reasons. One, because without them, it is a really great time for people who don’t indulge in gluten to get on the gratin train (which is usually either bolstered with a roux made from flour, covered in nonnegotiable bread crumbs, or both); and two, I think this gratin is really, really good (and, superficially, more beautiful) without them. So good in fact, I couldn’t choose between the two preparations, but would rather saddle you with this Sophie’s Choice. Alternatively, make both versions and then decide for yourself.
DO AHEAD Gratin (sans bread crumbs) can be baked 2 days ahead, then kept covered and refrigerated. To reheat, place in a 400°F. oven, uncovered (adding bread crumbs, if using), until returned to its bubbling, golden state, 10 to 15 minutes.