Bring a pot of salted water to a boil. Blanch broccoli for 2 minutes, then transfer to an ice bath to stop cooking. Drain and set aside.
Sauté onion and butter in a saucepan on medium heat until onion is translucent.
Whisk in flour, cooking for 2 minutes. Slowly stir in milk, continuing to whisk until sauce is thick and bubbly.
Remove heat and add salt, garlic powder, mustard powder, paprika and pepper. Add 1 cup of cheese, stirring until melted.
In a large mixing bowl, combine broccoli, cooked rice, and cheese sauce. Add any additional seasonings to taste.
Spread in a 2 qt. greased casserole dish. Top with remaining cheese and bake at 350°F for 35 minutes or until cheese is bubbly and slightly brown. Cool slightly before serving.
Notes
Time Saving Tip - You can skip the first step by swapping out fresh broccoli for an equal amount of frozen broccoli florets that have been thawed ahead of time!