Prepare the cauliflower: Rinse the cauliflower and cut it into small, bite-sized florets so they cook evenly and are easy for kids to eat. Pat dry with a clean towel if very wet.
Cook the cauliflower: Bring a large pot of salted water to a boil. Add the cauliflower florets and cook for about 5–7 minutes, until just fork-tender but not mushy. Drain well and let sit in the colander for a few minutes so excess moisture can escape. (You can gently pat dry with paper towels to keep the casserole from getting watery.)
Make the cheesy sauce: In a large skillet over medium heat, melt the butter. Add the minced garlic and cook for about 30 seconds, just until fragrant. Turn the heat down to low and stir in the cream cheese until it melts and becomes smooth.
Whisk in the sour cream and heavy cream, stirring until the mixture is creamy and well combined. Add 1 cup of the shredded cheddar, the mozzarella, and the Parmesan. Stir until the cheeses are melted and the sauce is smooth.
Season the sauce: Stir in the salt, black pepper, onion powder, and smoked paprika (if using). Taste and adjust seasoning as needed—this is your chance to make it as flavorful as you like.
Combine cauliflower and sauce: Add the drained cauliflower florets to the skillet (or transfer everything to a large mixing bowl if that’s easier). Gently fold the cauliflower into the cheese sauce until every piece is coated.
Assemble the casserole: Spoon the cheesy cauliflower mixture into the prepared baking dish, spreading it out evenly. Sprinkle the remaining 1/2 cup shredded cheddar over the top.
Bake: Place the casserole in the preheated oven and bake for 20–25 minutes, or until the top is bubbly and lightly golden around the edges.
Optional broil: If you like a deeper golden, slightly crisp top, switch the oven to broil for 2–3 minutes at the end. Watch it closely so it doesn’t burn.
Garnish and serve: Remove from the oven and let the casserole rest for about 5 minutes so it can set slightly. Sprinkle with chopped parsley or chives before serving. Scoop into bowls or onto plates and enjoy while warm and melty.
