Preheat your oven to 350°F and grease a 9-inch springform pan with butter. In a medium bowl, combine the finely ground almond flour, 1/2 cup sugar substitute, 3/4 teaspoon sea salt, and ground cinnamon. Pour in the melted and cooled butter, stirring until the mixture resembles wet sand and holds together when pressed. Press this mixture firmly into the bottom of your prepared pan, creating an even layer. Bake for 20-25 minutes until the crust is lightly golden and set, then remove and let cool while you prepare the filling.

While the crust cools, reduce your oven temperature to 325°F. In a large bowl, beat the softened cream cheese and 3/4 cup sugar substitute together until smooth and creamy, about 2-3 minutes. Add the room-temperature eggs one at a time, beating well after each addition to avoid overmixing and incorporating excess air. Gently fold in the vanilla extract, 1/4 teaspoon salt, sour cream, and lemon zest, stirring just until combined—I find that overmixing at this stage can lead to cracks in the finished cheesecake, so take your time and be gentle.

Pour the filling mixture from Step 2 over the cooled crust from Step 1, smoothing the top with a spatula. Bake at 325°F for 35-45 minutes until the edges are set but the center still jiggles slightly when you gently shake the pan—this residual heat will continue cooking the center as it cools. Once baked, turn off the oven and crack the door open about 2 inches, leaving the cheesecake inside for 1 hour to cool gradually. This slow cooling prevents the dramatic temperature shock that causes cracks. Then transfer the cheesecake to a wire rack and let it cool completely at room temperature for another hour before refrigerating.

While the cheesecake cools, prepare the fruit topping. In a medium saucepan, combine 1/2 cup water, 1/2 cup sugar substitute, and 2 teaspoons lemon juice. Bring to a simmer over medium heat, stirring occasionally until the sweetener dissolves. Add the sliced rhubarb and cook for about 5 minutes until it begins to soften, then add the quartered strawberries and continue cooking for another 5-10 minutes until the fruit is tender and the sauce has thickened slightly. I like to taste the sauce at this point and add a tiny pinch of salt if needed—it really brings out the fruity flavors. Remove from heat and stir in the 1 tablespoon unsalted butter until melted and incorporated.

Allow the strawberry-rhubarb sauce from Step 4 to cool to room temperature—if you prefer a smoother topping, you can blend it partially with an immersion blender or food processor at this point, or leave it chunky for texture. Once both the cheesecake and sauce are completely cooled, spread or spoon the topping evenly over the chilled cheesecake. Refrigerate for at least 2 hours before serving to allow the flavors to meld and the cheesecake to firm up for clean slicing.