Preheat the oven: Set to 375°F (190°C). Lightly grease a 9x13-inch baking dish.

Prep the cauliflower: Cut into bite-size florets. Aim for evenly sized pieces so they cook at the same rate.

Par-cook the cauliflower: Steam or microwave until just tender-crisp, about 4–6 minutes. It should still have a little bite. Drain well and pat dry with a clean towel to remove excess moisture.

Make the creamy base: In a large skillet over medium heat, warm the olive oil or butter. Add the garlic and cook 30 seconds until fragrant.

Stir in the dairy: Lower the heat and add cream cheese and sour cream. Stir until smooth and melty, 2–3 minutes.

Season the sauce: Add ranch seasoning, onion powder, smoked paprika, and black pepper. Pour in the chicken broth to loosen the sauce until it’s pourable but still thick. Taste and add salt if needed.

Fold in the chicken: Add the shredded chicken, 3/4 cup cheddar, and 1/2 cup mozzarella. Stir until everything is coated and combined.

Add the cauliflower: Gently fold in the par-cooked cauliflower so it’s evenly coated with the sauce. If using bacon, stir in half now and save half for topping.

Transfer to the dish: Spread the mixture into the prepared baking dish. Top with the remaining cheddar and mozzarella. Sprinkle on the remaining bacon if using.

Bake: Bake uncovered for 22–28 minutes, until bubbly around the edges and the top is lightly browned. For extra color, broil for 1–2 minutes, watching closely.

Rest and garnish: Let the casserole rest 5–10 minutes before serving. Garnish with chopped chives or parsley.