01 - Preheat oven to 375°F (190°C). Grease a 9x13-inch (23x33 cm) baking dish.
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.
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, until cheeses are 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.
06 - Sprinkle the remaining ½ cup cheddar cheese over the top.
07 - Bake for 20–25 minutes, until golden and bubbly.
08 - Let cool for 5 minutes. Garnish with chopped parsley before serving.