Make your favorite pumpkin pie recipe (like this one from Everyday Food - below). Double the recipe which should give you enough filling for roughly 20 little mason jars. Fill the jars, stopping about 3/4" from the top. Bake at the usual temperature, but start watching them carefully after about 25 minutes since they won't take as long to bake as a pie. Pull them out when the center seems set (about 35 minutes depending on oven variance). Let cool for an hour or so, then throw them in the fridge while you make the whipped cream.
Pumpkin Cream Pie DOUBLED RECIPE, via Everday Food Serves 20