Preheat the oven to 325ºF and lightly grease an 8x8 glass or ceramic baking dish. (see Tip for Success).
In a large bowl, combine the almond flour, sweetener, coconut flour, baking powder, and salt. Stir in the butter, egg, and lemon zest until well combined.
Press this mixture into the bottom and partway up the sides of the prepared baking pan.
In another large bowl, beat the cream cheese and butter together until smooth. Beat in the sweetener until well combined.
Beat in the egg, lemon zest, lemon juice, and lemon extract. Stir in the blueberries by hand.
Pour the filling over the crust. Bake 30 to 35 minutes, until the filling is mostly set, but the center still jiggles, and the edges are just golden brown.
Remove and let cool, then dust with powdered sweetener and cut into bars.
