Toss cauliflower florets with olive oil. Season with salt and pepper to taste.
Spread evenly on a baking sheet and roast 15-20 minutes or until tender. Remove from oven and reduce temperature to 375°F.
In a medium saucepan bring the heavy cream, garlic, salt, and pepper to a boil. Reduce heat and let simmer for 2 minutes or until the sauce starts to thicken.
Remove from heat and whisk in parmesan cheese and 1 cup of white cheddar cheese.
Spread roast cauliflower in 2 quart casserole dish. Pour cheese sauce over the cauliflower and top with remaining white cheddar cheese. Bake 15-20 minutes or until cheese is golden and bubbling.