Prep the pan. Line a 12-cup muffin tin with paper liners. Preheat the oven to 325°F (163°C).
Make the crust. In a bowl, mix 1 cup almond flour, 2–3 tbsp powdered sweetener, a pinch of salt, and 3 tbsp melted butter.
Stir until it resembles damp sand and clumps when pressed.
Press and par-bake. Divide the crust mixture among the 12 liners (about 1 tbsp each). Press firmly with your fingers or the bottom of a measuring cup. Bake 6–8 minutes until lightly golden at the edges.
Let cool while you make the filling.
Beat the cream cheese. In a mixing bowl, beat softened cream cheese on medium speed until smooth and fluffy, 1–2 minutes. Scrape the bowl well.
Add sweetener and flavor. Add 1/2–3/4 cup powdered sweetener (adjust to taste), 2 tsp vanilla, lemon zest if using, and a tiny pinch of salt. Beat until smooth, 30–60 seconds.
Blend in sour cream. Mix in 1/3 cup sour cream (and optional 1–2 tbsp melted butter for extra silkiness).
Beat on low until combined.
Add eggs last. Add eggs one at a time, mixing on low until just incorporated. Do not overbeat. Overmixing adds air and can cause cracks.
Fill the cups. Divide the batter evenly among the crusts, filling each liner almost to the top.
Tap the pan gently on the counter to release air bubbles.
Bake gently. Bake at 325°F (163°C) for 15–18 minutes. The centers should be slightly jiggly like set Jell-O, not liquid. The edges may look just set and matte.
Cool slowly. Turn off the oven, crack the door, and let the cheesecakes sit for 10 minutes.
Then move the pan to a rack and cool to room temp.
Chill to set. Refrigerate at least 2 hours, preferably 4+ hours or overnight. They firm up and taste better fully chilled.
Top and serve. Add a few fresh berries, a dusting of powdered sweetener, or a drizzle of sugar-free chocolate. Peel off the liner and enjoy.