Place pumpkin purée in a large mixing bowl with the rest of the ingredients. Mix well to combine.
Preheat oven to 425 °F. Lightly grease an 8” x 8” casserole dish with vegetable oil. Place pumpkin mixture in the dish and spread evenly. Bake for 10 minutes.
Lower oven temperature to 350°F and continue baking until custard is set, about 30- 35 minutes more. Test the center of the custard by inserting a paring knife in the center. If it comes out clean, the custard is done.
Place casserole dish on a wire rack, allowing the custard to cool for about 30 minutes. Cover the dish with plastic wrap and place it in the refrigerator until ready to serve.
Notes
To serve: Cut custard into 9 pieces. Place individual pieces on small plates. Top with whipped cream and sprinkle with a little cinnamon.