Mix bacon, 1/2 cup cheese, and parsley in small bowl. Set aside for topping.
Heat oven to 350 degrees. Bring 4 quarts water to boil in large pot. Add 1 tbsp salt and cauliflower, cook until tender. Drain and rinse with cold water. Transfer half to cutting board and roughly chop.
Melt cream cheese on low heat. Stir in heavy cream and remaining 2 1/2 cups of cheddar, cook until starts to melt.
Off heat stir in sour cream, cauliflower, 1/2 tsp salt and pepper. Transfer to a 2 quart baking dish, sprinkle with topping, and bake until brown and bubbly, about 15 minutes.