Preheat oven to 400F. Bring a large pot of salted water to a boil and cook cauliflower florets for 5 minutes until just tender. Drain very well and pat dry with paper towels.
In a saucepan over medium heat, melt butter and add heavy cream and cream cheese. Whisk until smooth and bubbling lightly, about 3 minutes.
Stir in dijon mustard, garlic powder, onion powder, paprika, salt, and pepper.
Reduce heat to low and gradually whisk in 1.5 cups cheddar and the gruyere until the sauce is silky and thick.
Fold the cauliflower into the sauce until every piece is coated, then transfer to a greased baking dish.
Top with remaining 1/2 cup cheddar and the crumbled bacon.
Bake for 18-20 minutes until bubbly, then broil 1-2 minutes for a golden crust. Rest 5 minutes before serving.