Prep the pan and oven: Line a 12-cup muffin pan with paper liners. Preheat the oven to 325°F (163°C). This slightly lower temperature helps the filling stay silky.

Make the crust: In a bowl, whisk almond flour, sweetener, and salt. Stir in melted butter, vanilla, and optional lemon zest until the mix resembles damp sand and clumps when pressed.

Portion and press: Divide the crust mixture evenly among the liners (about 1 heaping tablespoon each). Press firmly with the bottom of a measuring cup to create a compact base.

Par-bake the crust: Bake for 8–10 minutes until lightly golden at the edges. Set aside to cool slightly while you prepare the filling.

Beat the cream cheese: In a large bowl, beat cream cheese on medium speed until very smooth, about 1–2 minutes. Scrape the bowl. Smooth cream cheese prevents lumps later.

Add sweetener and flavor: Mix in powdered sweetener, lemon zest, vanilla, and salt. Beat until combined and fluffy, 30–60 seconds. Add lemon juice and beat just to blend.

Blend in eggs and sour cream: Add eggs one at a time on low speed, mixing just until incorporated. Fold in sour cream by hand to avoid overmixing. The batter should be creamy and pourable.

Fill the cups: Divide the filling among the crusts, filling each liner nearly to the top. Tap the pan gently on the counter to release air bubbles.

Bake: Bake at 325°F for 15–18 minutes. The centers should look slightly jiggly with set edges. Avoid browning on top.

Cool gradually: Turn off the oven, crack the door, and let the cupcakes sit for 10 minutes. Move the pan to a rack and cool to room temperature.

Chill to set: Refrigerate at least 2 hours (overnight is best). Top with whipped cream, a sliver of lemon, or berries just before serving.