Preheat oven to 375 degrees.
Combine 2 tablespoons butter with bread crumbs and set aside.
Boil cauliflower in a large pot for 2 minutes. Add in broccoli and cook an additional 2 minutes or until tender crisp. Drain well.
In a saucepan, melt 2 tablespoons butter. Add in flour, stirring until smooth. Add milk whisking constantly over medium heat until thick and bubbly. Stir in salt, cream cheese, garlic powder, black pepper and mustard powder until smooth. Add in cheddar cheese. Toss with broccoli and cauliflower.
Top with breadcrumbs mixture and bake at 375 degrees for 20-25 minutes or until heated through.