In a large pan over medium-low heat, melt your butter with your marshmallows, stirring constantly. Just before the marshmallows have melted all the way (there will still be some smaller lumps), remove the pan from the heat and quickly stir in vanilla extract and pumpkin pie spice. Next, quickly stir in crisped rice cereal until completely coated in marshmallows, then quickly fold in 1 heaping cup of marshmallows and gently press mixture into prepared pan (don't pack it down too much). You may need to butter your hands for this part. Let set, lift from the pan using the parchment paper, then slice and serve.
