Preheat oven to 400°F. Grease a 2 quart baking dish.
Rinse cauliflower and broccoli and cut into bite-sized pieces. Pat dry with paper towel.
In a large bowl, toss cauliflower and broccoli together with oil, and salt & pepper to taste. Place veggies on baking sheet and roast 12-15 minutes or just until tender-crisp
Meanwhile, in a large skillet, heat cream, chicken broth, mustard and garlic powder over medium heat. Simmer 3-4 minutes or until slightly thickened.
Add cream cheese to skillet and whisk until smooth.
Remove sauce from heat, stir in cheddar cheese and whisk until smooth. Taste and season with salt and pepper.
Place the roasted veggies into the prepared dish. Pour the cheese sauce overtop, and toss together.
Top with parmesan cheese and bake until bubbly and browned on top, about 20 minutes.
Notes
*To save prep time, use frozen broccoli and cauliflower. Mix them both in a colander in the sink and allow them to thaw and thoroughly drain before adding in Step 3.