1. Preheat the oven to 350 degrees.
2. Place 1 bag of frozen cauliflower in a glass baking dish.
3. Season with salt and pepper.
4. Follow with a layer of sliced onion and half of the cheddar cheese.
5. Place the other bag of cauliflower on top and sprinkle with the rest of the cheese.
6. Pour the whipping cream over the cauliflower.
7. Fill the whipping cream carton with water and add it to the cauliflower mixture.
8. Cover and bake for about 45 minutes to 1 hour.