Preheat oven to 350. Spray a 8x8 metal pan with cooking oil.
Combine the crust ingredients: almond flour, coconut flour, maple syrup, melted coconut oil, vanilla and salt in a bowl. Mix well using a fork until combined.
Add the mixture to the pan and press it down into an even layer using your hands. Bake for 16-17 minutes until golden brown.
While the crust is baking, combine the eggs (+ yolk), maple syrup, lemon juice, lemon zest, and vanilla in a bowl. Whisk very well until combined. You can also use an electric mixer to ensure the egg is well combined. Add the tapioca flour last and continue to mix until combined.
When the crust comes out of the oven, pour the egg and lemon mixture over top right away. Reduce the oven temp to 325. Bake for an additional 19-20 minutes until the top is mostly set.
Let the bars cool in the pan for 30 minutes, then transfer the pan to the fridge for at least 2 hours. Slide a knife around the edges of the bars to loosen, then cut into 9 square pieces. Sprinkle with organic powdered sugar, if desired. Serve and enjoy!