Spray a 9" pie plate with nonstick cooking spray, then set it aside.
Add 4 ounces (about 2 cups) of marshmallows and 1 1/2 tbsp of butter to a large, microwave safe bowl. Heat on HIGH for 45 seconds then stir well. Heat for another 30 seconds, then stir again until evenly combined and smooth. Stir in half the vanilla.
1 10 oz bag marshmallows, 4 tbsp salted butter, 1 tsp vanilla extract
Add 1 cup of the cereal and the graham cracker crumbs to the marshmallow mixture, then stir everything together until evenly combined. Transfer the mixture to the prepared pie plate.
4 cups rice krispie cereal, 1/2 cup graham cracker crumbs
Working quickly because it will harden fast, spray clean hands lightly with nonstick cooking spray, then press the mixture around the edges of the dish to create a 1" thick 'crust'. Set aside.
Add the rest of the marshmallows and butter to another large, microwave safe bowl. Heat on HIGH for 60 seconds, then stir well.
Microwave for another 30 seconds, then stir again until smooth. Add the rest of the vanilla, the food coloring, and pie spice then stir everything together until evenly combined. Add the rest of the cereal, then stir again until evenly incorporated and well coated.
3-4 drops orange food coloring, 1 1/2 tsp pumpkin pie spice
Transfer the sticky cereal mixture to the center of the dish and, again using clean hands lightly sprayed with nonstick spray, press out in an even layer to 'fill' the pie.
Set the pie aside and let it rest for 30 minutes to firm up.
Slice, serve, and enjoy!