Spray a 9x13-inch casserole dish with cooking spray and preheat the oven to 350 F.
Heat a large skillet over medium-high heat, and brown the ground beef with the chopped onion until no pink is left in the meat. Season with ½ tsp salt and pepper.
In a large bowl, mix the cabbage, rice, and tomato sauce until well combined. Season with 1 tsp salt and pepper to taste.
Transfer half of the cabbage mixture to the baking dish.
Spoon the ground beef evenly over the cabbage mixture.
Top with the remaining half of the cabbage mixture
Pour the beef broth evenly over the casserole sprinkle the fresh thyme and place the bay leaves on top.
Cover with foil and bake for 1 hr 20 minutes. At the 50-minute mark, remove the casserole from the oven, take off the foil, stir everything to ensure proper cooking, cover with foil again, and continue cooking until the rice is cooked through.