Preheat oven to 325F and lightly grease a 9" x 13" glass or ceramic baking dish (metal is not recommended).
In a large bowl, combine the almond flour, granulated sweetener, baking powder, and salt. Add the melted butter, egg, and vanilla extract, and stir well to combine. Transfer mixture to the prepared baking dish and press into the bottom and up the sides.
Press this mixture into the bottom and up the sides of the prepared baking dish.
Pumpkin Filling
In a large bowl, use an electric mixer to beat the cream cheese and softened butter until smooth. Beat in the powdered and brown sweeteners until well combined, then beat in the pumpkin, eggs, pumpkin pie spice, and vanilla until smooth.
Pour the filling over the crust. Bake 50-60 minutes, or until the sides are set about 2 inches from the edges of the pan, while the center is still a little jiggly.
Remove the cake from oven and let cool completely before cutting into squares. Top with lightly sweetened whipped cream if desired.
Notes
Storage Information: Store the cake, tightly covered, in the fridge for up to 5 days. It can also be frozen for several months. Make sure to wrap it up tightly to avoid freezer burn.