Preheat oven to 400 degrees.
To a large pot over high heat, add the chicken broth. Place the head of cauliflower into the broth, cover the pot, and bring to a boil. Reduce the heat and simmer, steaming the cauliflower for 10 minutes. Transfer the steamed cauliflower to a cast iron skillet. Season it with salt and pepper. Ladle about half of the broth from the pot over the cauliflower. In a small dish, stir together the melted butter, garlic, and lemon. Drizzle the butter mixture over the head of cauliflower. Add 4 thyme sprigs to the pan. Place the skillet into the preheated oven and roast for 10-15 minutes, until tender-crisp and golden on the outside. Note: if you’d like more color, turn the broiler on high for 2-3 minutes, or until desired color os achieved.
To serve, slice wedges of cauliflower and transfer them to serving plates. Spoon the pan juices over the cauliflower wedges. Serve promptly.