In a medium-size mixing bowl, whisk together half & half, flour and gelatin. Whisk until flour and gelatin crystals have dissolved. Add eggs, whisking until combined.
Add sugar, pumpkin puree, pumpkin pie spice, nutmeg, cinnamon and salt. Whisk until smooth.
Pour the mixture into a stove top pot and cook over medium heat stirring gently to prevent sticking.
Cook for 5 minutes until the custard is the consistency of thick pudding. Remove from the heat. Add butter and vanilla, mixing until combined.
Pour custard into baked shell and smooth the top. Cool on the counter for 1 hour.
Chill in the refrigerator uncovered for at least 4 hours before cutting.
Top with a dollop of fresh whipped cream.
Notes
This pie can also be made with sugar substitute in equal amounts.