Thinly slice the onions, season with salt, and sauté in olive oil until soft. Set aside.
Cut the cabbage into wedges, season with salt, and sear on both sides in plenty of olive oil until golden. Use a second pan to press the wedges for the best results.
In a jug, combine the cream and stock.
Layer the cabbage and onions in a heatproof casserole dish or cast iron skillet. Pour over the cream mixture, add cheeses, thyme sprigs, and season with salt and pepper.
Roast at 200°C for 20-30 minutes, until bubbly and golden on top.
