Line an 8-inch square baking dish with unbleached parchment paper.
Combine the almond flour, powdered xylitol, and sea salt in a large bowl. In a medium bowl, stir together coconut oil, butter, and vanilla extract.
Stir the wet ingredients into the dry until thoroughly combined.
Press the dough evenly into the bottom of the prepared baking dish.
Bake for 15 –17 minutes until lightly golden.
While the crust bakes, prepare the topping. In a blender or food processor (or by hand with a whisk), combine the almond flour, powdered xylitol, stevia, eggs, and lemon juice. Blend on medium speed until smooth.
Remove the crust from the oven. Pour the topping evenly over the hot crust
Pop back into oven. Bake for 15–20 minutes at 350° F until the topping is golden at edges.
Let cool in the baking dish for 30 minutes, then refrigerate for 2 hours to set.
Put 1⁄4 cup xylitol in a coffee grinder until powdery with the same consistency of icing sugar. Sprinkle with powdered xylitol (optional). Cut into bars and serve.