1. Begin by making the crust. Preheat oven to 350F. Grease an 8" × 8" glass baking dish, or fully line with parchment paper.
2. In a large bowl, stir together softened coconut oil, confectioners sugar, and vanilla. Add flour and salt and mix until crust is formed.
3. Transfer the mixture to the prepared baking dish. Press the crust evenly into bottom of the baking dish, and up the edges about an inch. This will prevent the filling from going beneath your crust.
4. Refrigerate for 30 minutes.
5. Bake for about 25-30 minutes, or until light golden brown. While crust is baking, prepare your filling.
6. In a large bowl, whisk together the melted butter, sugar, lemon juice, and lemon zest.
7. In a separate bowl, stir together All Purpose Flour, baking powder, and salt.
8. Whisk the dry ingredients into the wet until combined.
9. When the crust is out of the oven, pour the filling on top while the crust is still warm.
10. Bake for 18 - 20 minutes, or until bubbles have formed all over the top, and the bars have begun to set. The middle may still be a bit jiggly, but will set up more as the pan cools.
11. Cool completely in the pan on a wire rack, or chill in refrigerator.
12. Cut into 16 2" x 2" squares with a sharp knife. Serve chilled, dusted with confectioners sugar immediately before serving.