Bring a large pot of salted water to a boil.
Cut the cauliflower into 1 inch pieces.
Peel the potato and cut into 1/2 inch pieces.
Add the cauliflower, potato and garlic to the boiling water. Continue to boil for 16-20 minutes, or until the vegetables are soft, but not falling apart.
Drain well in a colander and shake dry.
Add the cauliflower, potatoes, and garlic to the bowl of a food processor and process until smooth and creamy. Add butter, milk, and 4 tablespoons of the cheese. Process until very smooth.
Add salt and pepper to taste. Serve immediately, sprinkled with the remaining Parmesan cheese.
NOTE: If you are making the mixture ahead of time, spoon into a shallow casserole dish sprinkled with the cheese. Bake at 350° until heated through and golden.