In a large pot over medium low heat, melt the butter and the marshmallows together. Once melted, stir in the vanilla.
Then quickly stir in the cake mix, then the Oreos, then the rice cereal. Once combined, quickly pour into the pan.
While still hot, top with the sprinkles. Let set, and then slice and serve.
Notes
Krispie Treats taste best when eaten within one or two days of making. Make sure to store in an air tight container once cooled.
For easier mixing, spray a spatula with cooking spray.