Preheat the oven to 325°F. In a medium-sized bowl, combine the almond flour, salt, and baking soda.
In a separate small mixing bowl, combine the maple syrup and vanilla extract. In a small saucepan, melt the palm oil shortening, and add it to the wet ingredients. Stir the wet ingredients into the dry ingredients and mix until evenly combined.
Pat the dough into a 9-inch tart pan and bake for 10-15 minutes or until golden. Remove the crust from the oven to cool.
Make the filling:
In a medium-sized mixing bowl, whisk the egg yolks and maple sugar together until smooth. Whisk in the lemon juice and most of the zest. (Reserve some of the zest for garnish.) In a double boiler, heat the mixture, whisking constantly until thick.
Remove the filling from the heat, and whisk in the butter. Pour the filling into the center of the tart crust, and bake for 15 minutes at 325°F.
Remove from the oven, allow to cool, and garnish with lemon zest and fresh berries. Refrigerate until serving.