Combine crushed Cocoa Puffs and butter until the cereal is moistened. Press into tartlet pans. Bake at 350 for 10 minutes. Allow to cool before popping out of pans.
In a saucepan, combine pumpkin, ½ cup heavy cream, sugar, and pumpkin pie spice. Bring to a boil, lower temperature, and allow to boil for 5 minutes. Remove from heat. Cool completely before proceeding.
Beat remaining 1 cup of heavy cream and vanilla to stiff peaks. Fold in pumpkin mixture. Pipe (or spoon) the mousse into the tartlet shells. Serve cold. Make 16 tartlets.