Step 1: Line an 8x8 or 9x9 inch square baking pan with parchment paper and lightly grease with butter or non-stick spray.
Step 2: In a large pot or dutch oven, melt the butter over low heat.
Step 3: Once the butter is melted, whisk in the pumpkin puree until smooth and well combined with the butter.
Step 4: Add the mini marshmallows, pumpkin pie spice, salt, and vanilla extract. Stir continuously over low heat until the marshmallows are almost completely melted.
Step 5: Remove the pot from the heat and continue to stir until the mixture is completely smooth.
Step 6: Gently fold in the Rice Krispies cereal using a spatula until every piece is evenly coated in the orange marshmallow mixture.
Step 7: Transfer the mixture to the prepared pan. Using buttered fingertips, gently pat the mixture into an even layer without pressing down too firmly.
Step 8: Allow the treats to cool and set at room temperature for at least 1 hour before slicing into 16 squares.