Preheat oven to 350°F. Bake potatoes for about an hour, or until cooked through.
Toss Cauliflower florets in melted butter, then roast in same oven as potatoes until lightly browned and tender crisp, about 15 minutes.
Meanwhile, cook bacon until evenly crisp. Drain, crumble and set aside. Briefly sauté 3/4 of the sliced green onions in what bacon drippings are left in skille after draining.
When potatoes are cooked, divide each in half and scoop flesh into a large bowl, saving the skins. Mix together roasted cauliflower, sour cream, milk, salt, pepper, 2/3 cup cheddar, feta and sautéd green onions and bacon. Blend with a hand mixer until creamy, or with a potato masher if you like coarser.
Top with remaining cheddar and green onions
Bake in oven until filling is cooked through, and the cheese is melted and golden brown to crispy, about 15-20 minutes.
Note: there will be extra filling, thanks to the added cauliflower – you can save that for another day – try frying it tomorrow for lunch.