Preheat the oven to 325°F. Spray a 9-inch pie dish or pan with cooking spray and set it aside.
In a large mixing bowl, whisk together the pumpkin puree, brown sugar substitute, sugar substitute, and pumpkin pie spice until combined.
Pour in the evaporated milk and vanilla extract and whisk carefully until smooth.
Beat in the eggs, one at a time, then beat in the egg yolk until just combined.
Pour the pumpkin into the greased pie dish, and bake on the middle rack of the oven for 1 hour or until the pie is mostly set. It's okay if the center is still slightly jiggly.
Let the pie rest on a cooling rack for at least 1 hour or until room temperature before wrapping with plastic wrap and chilling in the fridge for at least 4 hours.
Serve chilled with sugar-free whipped cream, if desired.