Preheat the oven to 350°F (175°C).
In a medium bowl, combine almond flour, coconut flour, powdered sugar, melted butter, and salt. Mix until crumbly.
Press the crust mixture into the bottom of an 8x8-inch baking dish.
Bake the crust for 15 minutes until lightly golden.
In a large bowl, whisk the eggs until beaten. Add granulated sugar, fresh lemon juice, lemon zest, and baking powder. Mix until smooth.
Pour the lemon filling over the baked crust and spread evenly.
Bake for an additional 20-25 minutes until the filling is set and edges are lightly golden.
Let the bars cool completely at room temperature, then refrigerate for at least 120 minutes before serving.
Cut into squares and dust with powdered sugar before serving.