Preheat the oven to 450 degrees F (232 degrees C).
In a large bowl, toss the cauliflower florets with butter. Season with sea salt and black pepper.
Transfer the cauliflower to a small 1.5 quart (1.4 L) casserole dish in a single layer. (Line the pan unless it's glass or stoneware. If there's too much cauliflower to fit in a single layer, roast on a larger baking sheet instead.) Roast in the oven for 15 minutes, until crisp-tender.
Meanwhile, in the same bowl, whisk together the sour cream and heavy cream, until smooth. Stir in the minced garlic, half of the cheddar cheese, half of the bacon bits, and half of the green onions. If desired, season sauce with sea salt and black pepper.
When the cauliflower is done roasting, take it out and leave the oven on. Add the cauliflower to the bowl and mix with the sauce.
Return the cauliflower mixture to the casserole dish. Top with remaining cheese and bacon bits.
Bake for 10 minutes until the cheese melts. Top with remaining green onions.