Prepare a 9x9 inch pan with parchment paper or foil. If using foil, spray with a non-stick spray.
Melt ½ cup butter over medium heat in a large non-stick pot. Add marshmallows and as they melt, stir well to mix with the butter.
Remove from heat, add chocolate chips and vanilla. Stir until combined.
Add Rice Krispies and mix until coated.
Press mixture into pan using greased hands. Do not press too hard, just enough to keep it together.
Allow to cool, then remove from pan with parchment paper (or foil) and cut into squares.