This recipe is based on my adoration for the classic cream-based gratin spotlighting a single seasonal vegetable. It is dairy rich and vegetarian, but I would not blame you if you wanted to toss some lardons (browned bacon bits) into the casserole with the browned cabbage before baking. This simple but luxurious treatment is my homage to green cabbage, which I will never look at the same way again.
Stand the cabbage on its stem end and cut it into slabs 1 to 1 1/2-inches thick. Lay the slices flat and cut them in half and then cut a V shape into the thickest part of the core while leaving the leaves intact. Season the slices generously with 1 1/2 teaspoons of the salt and 1/2 teaspoon of the pepper.
Heat the oil in your largest sauté pan over medium-high heat. Working in batches, cook the cabbage slices until they are nicely browned, 4-5 minutes per side, turning them with a spatula and keeping the slices intact as best you can. Transfer the cooked cabbage slices to a 2- or 3-quart casserole dish (a 9 x 13 baking dish is 3 quarts) and repeat cooking the remaining slices.
Meanwhile, whisk the cream with the mustard, caraway, if using, the remaining 1/4 teaspoon salt and 1/8 teaspoon black pepper. Preheat the oven to 475°F.
When all the cabbage is cooked, cram it into the casserole dish in a single layer, including any stray strips that came off while cooking it. Tuck in the garlic and the bay leaf. Pour the cream over the cabbage and press it down with a spatula so this it is in an even layer. Sprinkle on the cheese to create a nearly solid layer on top. (The gratin can be prepared 2 days in advance and refrigerated up to this point.)
Bake the gratin until it is bubbling and well browned on top, 25 to 30 minutes. For the most even browning, rotate the casserole dish during the last 10 minutes of baking.