This diabetic-compatible tart will remind you of evenings in a sidewalk café in Paris, minus the cigarette smoke.
In the bowl of a food processor, pulse the flour, almonds, sugar, salt, cinnamon, cardamom, if using, and baking powder to mix. Cut the butter into 8 pieces and add to the dry ingredients. Pulse until the mixture resembles coarse pea-sized bits. Add the egg and continue to pulse until the dough forms a ball that revolves on the blade (you may need to add 1-2 tablespoons iced water to make this work). Remove the dough, pat out to a disk, and wrap in plastic wrap. Refrigerate for 35-45 minutes.
Dust a work surface with flour. Roll out the dough to about a 14-inch circle. Place into a 9- to 10-inch fluted tart pan with a removable bottom. (This dough is fragile and will break, but you can just piece it back together with your fingers.) Refrigerate for 15-20 minutes before filling.
Preheat the oven to 350 degrees.
Beat the cream cheese in the bowl of a food processor or electric mixer until smooth. Add the granulated sugar substitute and beat until incorporated. Add the eggs 1 at a time, beating well after each addition. Add the lemon juice and beat until well mixed. Stir in the lemon zest by hand.
Pour into the crust and bake for 30 minutes. Transfer to a wire rack and let cool. Refrigerate for 2-3 hours.