Make the blueberry topping: Add blueberries, water, sweetener, and lemon juice to a small saucepan over medium heat.
Cook 5–8 minutes, stirring and lightly mashing some berries. If using xanthan gum, sprinkle a tiny pinch at a time and whisk until lightly thickened. Remove from heat and let cool completely.
Prepare the crust: In a bowl, mix almond flour, melted butter, sweetener, vanilla, and salt.
Stir until it looks like damp sand and clumps when pressed. Taste and adjust sweetness if needed.
Whip the cheesecake layer: In a mixing bowl, beat softened cream cheese with sweetener, vanilla, lemon zest, lemon juice, and salt until smooth. In a separate bowl, whip heavy cream to soft peaks.
Fold the whipped cream into the cream cheese mixture until light and fluffy.
Assemble: Spoon crust mixture evenly into jars and press lightly with the back of a spoon. Add a generous layer of cheesecake filling. Top each jar with cooled blueberry topping.
Chill: Cover and refrigerate at least 2 hours, or up to overnight, to set the layers and develop flavor.
Serve: Enjoy straight from the jar.
If you like, finish with a few fresh blueberries or a light sprinkle of lemon zest.