Preheat oven to 400°F. Grease a 2 quart baking dish.
Rinse cauliflower and cut into bite sized pieces. Toss with oil and salt & pepper to taste. Place on a baking sheet and roast 12-15 minutes or just until tender-crisp.
While cauliflower is cooking, bring cream, chicken broth, mustard and onion powder to a simmer in a large skillet. Let simmer 3-4 minutes or until slightly thickened.
Whisk in cream cheese until smooth.
Combine cheddar, parmesan, and gruyere cheese in a small bowl. Set ½ cup of the cheese mixture aside for topping.
Remove from heat and stir in the remaining 2½ cups of cheese. Whisk until smooth. Taste and season with salt and pepper.
Toss the cheese sauce and cauliflower together and place into the prepared dish.
Top with cheese and bake until bubbly and browned on top, about 20 minutes.
Notes
Break cauliflower into small pieces to resemble the size of macaroni.
Steamed, boiled or roasted cauliflower can also be used. If boiled or steamed, be sure to drain it well to prevent a watery sauce.