Prep the pan and oven: Preheat the oven to 325°F (165°C). Line the bottom of an 8- or 9-inch springform pan with parchment.
Lightly spray the sides with nonstick spray.
Make the crust: In a bowl, mix almond flour (or graham crumbs), erythritol, cinnamon, melted light butter, vanilla, and salt until sandy and slightly clumpy.
Press and pre-bake: Press the mixture evenly into the prepared pan. Bake for 8–10 minutes until lightly set and fragrant. Let it cool while you prepare the filling.
Beat the cream cheese: In a large bowl, beat the light cream cheese with a hand mixer on medium until smooth and fluffy, about 1–2 minutes.
Avoid overbeating.
Add sweetener and yogurt: Add erythritol and beat just to combine. Mix in Greek yogurt, vanilla, and salt until smooth.
Blend in eggs: Add eggs one at a time, mixing on low speed until just incorporated. Do not whip in extra air.
Finish the batter: Whisk cornstarch into the milk until no lumps remain, then beat into the batter on low.
Batter should be silky and pourable.
Flavor with cinnamon: Remove 1/2 cup of batter to a small bowl and stir in 1 teaspoon cinnamon. This will be your snickerdoodle swirl.
Assemble: Pour the plain batter over the cooled crust. Spoon the cinnamon batter in dollops on top.
Use a knife or skewer to gently swirl—fewer strokes make prettier swirls.
Bake low and slow: Bake at 325°F for 35–45 minutes, until the edges are set and the center still has a slight jiggle. The top should look matte, not wet.
Cool gradually: Turn off the oven, crack the door, and let the cheesecake sit inside for 30 minutes. Then remove and cool to room temperature.
Chill and finish: Whisk the cinnamon and erythritol for the topping.
Dust lightly over the cooled cheesecake. Cover and chill at least 4 hours, preferably overnight.
Slice smart: Run a thin knife around the edge before releasing the springform. For clean slices, use a hot, damp knife and wipe between cuts.