Preheat the oven to 325°F (165°C). Line an 8x8-inch square baking pan with parchment paper, leaving an overhang on two sides for easy lifting. Lightly grease the exposed sides of the pan.

In a medium bowl, combine the almond flour, 2 tablespoons of the granulated sweetener, and salt. Stir in the melted butter until the mixture looks like damp sand and holds together when pressed.

Transfer the crust mixture to the prepared pan. Press it firmly and evenly into the bottom using your fingertips or the bottom of a measuring cup to create a compact, level layer.

Bake the crust for 10–12 minutes, until lightly golden around the edges. Remove from the oven and let cool slightly while you prepare the cheesecake filling. Keep the oven at 325°F.

In a large mixing bowl, beat the softened cream cheese with an electric mixer on medium speed until completely smooth and creamy, about 2 minutes. Scrape down the sides of the bowl.

Add the powdered or granulated sugar-free sweetener and the remaining 1 tablespoon of granulated sweetener. Beat again until well combined and fluffy, 1–2 minutes. Taste and adjust sweetness if needed.

Add the vanilla and sour cream or heavy cream and mix on low speed just until incorporated and smooth.

Add the eggs one at a time, mixing on low speed after each addition just until blended. Do not overbeat once the eggs are added to avoid excess air and cracking.

Pour the cheesecake batter over the partially cooled crust. Smooth the top with a spatula and gently tap the pan on the counter to release any large air bubbles.

Bake at 325°F for 25–30 minutes, or until the edges are set and the center still has a slight jiggle when you gently shake the pan. The top should look just set, not browned.

Turn off the oven, crack the door open slightly, and let the cheesecake cool in the oven for 20–30 minutes to reduce the risk of cracking. Then transfer the pan to a wire rack and cool completely to room temperature.

While the cheesecake cools, make the strawberry topping. In a small saucepan, combine the sliced strawberries, water, and 2 tablespoons granulated sugar-free sweetener. Stir over medium heat until the berries release their juices and start to soften, 5–7 minutes.

In a small bowl, whisk the cornstarch (or glucomannan/xanthan) with 1–2 teaspoons of cold water to make a smooth slurry. Slowly stir the slurry into the strawberry mixture while it simmers gently.

Continue to cook, stirring frequently, until the topping thickens to a jammy, spoonable consistency, 2–4 minutes. Remove from the heat and stir in the lemon juice. Taste and adjust sweetness or lemon if needed.

Let the strawberry topping cool to room temperature. It will thicken more as it cools. If you prefer a smoother topping, lightly mash the berries with a fork; for chunkier texture, leave them mostly intact.

Once the cheesecake layer is completely cool, spread the cooled strawberry topping evenly over the surface. Gently level it with the back of a spoon or an offset spatula.

Cover the pan and refrigerate for at least 3 hours, or until fully chilled and firm. For best texture and clean slices, chill overnight.

To serve, use the parchment overhang to lift the chilled cheesecake slab from the pan onto a cutting board. Use a sharp knife wiped clean between cuts to slice into 16 squares. Garnish with extra fresh strawberry slices if desired.