In a large pot, melt the butter over medium-low heat. Add the marshmallows and 5–10 drops of orange food coloring. Stir until no white remains and the color is even, aiming for a deep pumpkin-pie orange. Turn off the heat. (If using pumpkin pie spice, stir it in now.)

Add the cereal and stir quickly until fully coated. Spray two 9-inch pie pans with nonstick cooking spray and divide the mixture evenly between them.

Spray the bottom of a dry measuring cup with nonstick spray and press the mixture into a flat, even layer in each pan. Press firmly but do not compact it aggressively.

Let the pans set on the counter for 1 hour, or refrigerate for 30 minutes.

Flip each pan upside down onto a parchment-lined baking sheet. Once released, turn the round right side up and slice into 8 wedges.

In a medium bowl, beat the softened cream cheese with a hand mixer until light and fluffy. Add the vanilla, then the powdered sugar one cup at a time, then the milk. Beat until thick and pipeable.

Transfer ⅓ cup of the frosting to a small zip-top bag and set aside.

Beat the peanut butter into the remaining frosting until smooth. Transfer to a second zip-top bag.

Snip a small corner off the plain cream cheese bag and pipe a small dollop in the center of each wedge.

Snip a small corner off the peanut butter bag and pipe a crust along the wide outer edge of each wedge. Serve.