Preheat the oven to 350°F. Lightly oil the bottom and sides of a 9x13” pan.
To make the crust: In a small bowl, combine the butter, ½ cup sugar, almond flour, and salt and mix until smooth. Press the crust mixture into the bottom and slightly up the sides of the pan. Bake for 20 minutes or until the edges are lightly browned. Remove and cool on wire rack for 15-20 minutes.
To make the filling: In a large bowl, combine eggs, 3 cups sugar, lemon zest, lemon juice, and coconut flour and mix well. Set aside.
Pour the filling onto the cooled crust and bake for an additional 30 minutes or until set. Let cool on wire rack.