01 - Preheat oven to 375°F and grease a 9x13-inch baking dish with butter or cooking spray.
02 - Bring a large pot of salted water to a boil. Add broccoli and cauliflower florets, blanch for 3–4 minutes until just tender. Drain well and pat dry with paper towels.
03 - In a saucepan over medium heat, melt the butter. Add the heavy cream and cream cheese, whisking until smooth and slightly thickened, about 2–3 minutes.
04 - Stir in 1 cup of cheddar cheese, Parmesan cheese, garlic powder, onion powder, paprika, salt, pepper, and nutmeg. Cook, stirring constantly, until cheeses are completely melted and sauce is creamy. Remove from heat.
05 - Spread the blanched broccoli and cauliflower evenly in the prepared baking dish. Pour the cheese sauce over the vegetables and gently toss to coat evenly.
06 - Sprinkle the remaining ½ cup cheddar cheese over the top. Bake for 20–25 minutes until golden and bubbly.
07 - Let the casserole cool for 5 minutes before serving. Garnish with chopped fresh parsley if desired.