Heat your oven to 425 F. Place the cauliflower, garlic, and onion into a roasting pan. Toss with olive oil, and salt and pepper to taste. Roast for 20 minutes, stirring 2-3 times.

While the veggies are still hot, place in a blender or food processor. While the blender is on, begin to drizzle in the milk, and process until smooth.

Begin adding the butter, little by little while pulsing the food process or running the blender on low - blend until the butter is incorporated.

If you want to get crazy creamy smooth texture, then pass the puree through a fine mesh sieve. It takes patience, but the result is worth it.