Preheat the oven to 400°F. Coat an 8 x 8- inch (or 11 x 7- inch) baking pan with nonstick spray.
Add in the rice, water, and onion soup mix into the pan and stir to combine.
Place the sliced butter on top of the mixture in the pan and cover tightly with aluminum foil.
Bake for 30 minutes, covered. Remove the foil and bake for an additional 30 minutes. *see note
Fluff rice with a fork and serve warm.
