Add half of the Cheez Whiz to the broccoli-rice mixture and stir well.
In a skillet, melt the butter over medium heat. Add chopped onion and celery to the melted butter, and cook until they are tender but not browned.
Stir in the cream of chicken soup and milk into the skillet with the onion and celery mixture. Season with salt and pepper to taste. Mix everything well.
Pour the creamy sauce over the broccoli and rice mixture into the casserole dish. Ensure the sauce is evenly distributed, and stir to combine.
Top the casserole with the remaining Cheez Whiz.
Bake in the preheated oven for 30 minutes, or until the casserole is hot and bubbly, and the top is golden brown.
Remove from the oven, let it cool slightly, and then serve your delicious Helen's Broccoli Casserole!
Enjoy your comforting and cheesy broccoli casserole!