1. Preheat the oven to 400° Fahrenheit (204° Celsius). Grease a 9 inch pie pan, then set the pan aside.
2. Whisk pumpkin puree, milk, vanilla, and optional egg in a large measuring cup or bowl.
3. Stir in the flour, sweetener, cinnamon, pumpkin spice, baking powder, salt, and optional corn starch until well mixed.
4. Smooth the mixture directly into the prepared pan. No crust required.
5. Bake on the center rack of the oven for 35 minutes or until the edges are set and the middle is slightly jiggly.
6. Let cool on a wire rack on the counter. Then refrigerate at least 6 hours or overnight, during which time the crustless pumpkin pie will firm up to an easily sliceable texture. Serve cold or hot, with whipped cream if desired.
7. Once the pie sets, refrigerate any leftovers covered tightly in the pan or in a lidded container for up to 5 days. Or freeze slices for up to 3 months and thaw before serving.