Melt marshmallows and butter either a) in a medium pot on the stove or b) in a large microwave-safe bowl. Remove from heat or the microwave and stir in rice krispies and graham crackers.
Press mixture evenly into a 9 by 12 inch pan lined with aluminum foil. Let cool until firm and then cut into squares.
Add white chocolate to a medium microwave safe bowl and heat in 20 second intervals until melted and smooth. Stir in cheesecake pudding mix until well incorporated, and then drizzle over rice krispie treats. Top with sprinkles, if desired.