Prepare the Cabbage: Start by cutting one medium green cabbage into thick wedges, keeping the core intact so the leaves stay together.

Sear the Cabbage: Melt 1 tablespoon (15g) of butter in a large oven-safe skillet or frying pan over medium-to-high heat. Place the cabbage wedges cut-side down in the hot skillet. Sear for about 5-6 minutes on each side until they are golden brown and slightly caramelized. Season generously with salt and black pepper while searing. Once seared, remove the cabbage wedges from the skillet and set them aside.

Sauté the Onion: In the same skillet, reduce the heat to medium-low. Add the finely sliced onion to the skillet and sauté for about 10 minutes until it becomes very soft and translucent. Season with a pinch of salt and black pepper.

Caramelize Onion with Balsamic: Melt the remaining 1 tablespoon (15g) of butter into the skillet with the onions. Stir in the balsamic vinegar and continue to cook for another 7 minutes, stirring occasionally, until the onion turns a deep golden brown and is beautifully caramelized.

Build the Sauce: Return the seared cabbage wedges to the skillet, arranging them amongst the caramelized onions. Pour in the beef broth and heavy cream. Add the fresh thyme sprigs (or sprinkle in dried thyme) and a good grinding of black pepper.

Bake to Perfection: Sprinkle the grated Gruyère cheese evenly over the cabbage and sauce.

Bake: Transfer the skillet to an oven preheated to 205∘C (400∘F). Bake for about 30 minutes, or until the sauce is bubbly, the cheese is melted and golden brown, and the cabbage is tender.

Serve: Carefully remove the skillet from the oven. Let it rest for a few minutes before serving.