The best way to ensure your cauliflower mashed potatoes will be thick and creamy is to limit the amount of liquid that goes into the mixture. You can do this by patting the cauliflower pieces dry after you drain them so there is no excess moisture when you combine the ingredients. If you find that it’s still too runny, you can try to thicken it up with a cornstarch slurry.  Mix the water and cornstarch together until smooth, then slowly incorporate a little at a time until the cauliflower mashed potatoes reaches your desired thickness!