Wash the cauliflower, towel dry, trim outer leaves and cut into florets, or just into chunks.
Place the cauliflower florets in a microwave-safe bowl. Add 2 tablespoons of water to the bottom of the bowl, cover with a microwave-safe plate and microwave on high for about 10 minutes, until very tender.
Meanwhile, place the butter, garlic, Parmesan, salt and pepper in your food processor's bowl.
When the cauliflower is cooked, carefully remove it from the microwave (bowl and plate will be hot and steam will escape) and transfer to the food processor. Process until very smooth, 1-2 minutes. Serve immediately.