Preheat oven to 350°F. Grease 9x13 casserole dish with nonstick spray.
Wash and dry the fresh broccoli, cut into florets. Place into large microwavable bowl with water and tightly cover with plastic wrap. Microwave for 5 minutes, let stand 2 minutes and drain. (If using frozen broccoli, steam for half the time given on the package directions, then drain.)
In a large bowl, combine the remaining ingredients except the crackers and butter. Add the broccoli to the bowl and mix to coat. Transfer to prepared baking dish.
Bake 20 minutes. Meanwhile, combine Ritz crackers and melted butter in small bowl. Remove casserole from oven and sprinkle Ritz topping evenly over top. Return to oven for an additional 10 minutes.
Store: Store leftovers in a covered dish in the fridge for up to 5 days.
Reheat: Reheat portions in the microwave.
Make-ahead: You can assemble broccoli cheese casserole the day before serving. Place the ingredients in the pan, minus the cracker topping, cover and store in the fridge overnight. The next day, place in the oven while it's preheating and bake an additional 5 minutes before adding the cracker topping.
Freeze: You can freeze the prepared broccoli casserole in a foil container tightly covered with plastic wrap. Allow to thaw overnight in the fridge before baking. Again, remove from fridge as oven preheats and allow an extra 5 to 10 minutes of baking time.