Prep the pan: Line the bottom of a 9-inch springform pan with parchment. Wrap the outside with two layers of heavy-duty foil to prevent leaks.
Heat the oven: Preheat to 325°F (163°C).
Set a kettle of water to boil for the water bath.
Make the crust: In a bowl, mix almond flour, sweetener, cinnamon, and salt. Stir in melted butter and vanilla until the mixture looks like damp sand.
Press and par-bake: Press the crust firmly into the bottom of the pan. Bake for 10 minutes, then let it cool slightly while you make the filling.
Cream the base: In a large bowl, beat the softened cream cheese on medium speed until completely smooth, about 2 minutes.
Scrape the bowl well.
Add sweetener and spices: Beat in the sweetener, pumpkin pie spice, cinnamon, and salt until combined and fluffy.
Mix in pumpkin: Add the pumpkin puree and beat just until incorporated. Don’t overmix.
Add eggs and sour cream: Beat in the eggs one at a time on low speed, mixing just until blended. Add sour cream and vanilla and mix on low until smooth.
Scrape the bowl as needed.
Fill the pan: Pour the batter over the par-baked crust. Tap the pan gently on the counter to pop surface bubbles.
Create the water bath: Place the springform pan in a large roasting pan. Pour hot water into the roasting pan so it comes about halfway up the sides of the springform.
Bake: Bake at 325°F (163°C) for 55–70 minutes.
The edges should be set and the center should have a slight wobble, like Jell-O.
Cool gradually: Turn off the oven, crack the door, and let the cheesecake sit inside for 30 minutes. This helps prevent cracks.
Chill: Remove from the water bath, unwrap the foil, and cool to room temperature. Cover and chill at least 6 hours, preferably overnight.
Release and serve: Run a thin knife around the edge, release the springform, slice with a hot, clean knife, and add whipped cream if you like.