Prep the cauliflower: Preheat your oven to 425°F (220°C).
Line a sheet pan with parchment. Toss the cauliflower florets with olive oil or butter, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Spread out in a single layer.
Roast until tender: Bake for 18–22 minutes, flipping once, until the edges are lightly browned and the florets are just fork-tender.
Don’t overcook; you want them to hold their shape.
Start the sauce: In a medium saucepan over medium heat, warm the heavy cream until it steams but doesn’t boil. Reduce heat to low and whisk in the cream cheese until smooth.
Add the cheese: Stir in cheddar and mozzarella a handful at a time, whisking until melted and silky. Add Dijon, garlic powder, onion powder, remaining salt and pepper, and a pinch of paprika or cayenne if using.
Combine: Transfer roasted cauliflower to a baking dish (8x8 or similar).
Pour the cheese sauce over and gently fold to coat every piece.
Optional bake for a crust: Sprinkle Parmesan on top. Return to the oven for 8–10 minutes until bubbly. For extra color, broil 1–2 minutes, watching closely.
Finish and serve: Let it sit 5 minutes to set.
Garnish with chives or parsley. Serve hot and enjoy that cozy, creamy goodness.