PREPARE ALMOND FLOUR CRUST: (Alternately, use your favorite tart crust. Store-bought puff pastry works well too!) Blend the almond flour, tapioca starch, salt, and sugar in a food processor or paddle mixer. Pulse or beat in the cold butter cubes until mixture is like coarse crumbs. Add the water 1 tsp at a time and pulse until dough just forms. Roll dough between two sheets of parchment paper, peel one side & replace, then peel the others side and turn over the pan. Refrigerate. FILLING: Preheat oven to 400°F (205°C). In a pan (preferably thick-bottomed), spread out the sugar and cubed butter. Bring to a simmer, then let simmer 5-7min over low heat without stirring. When mixture is a solid brown (not golden brown, and not very dark brown), pour into a quiche-style ceramic or glass pan. It's okay if it does not look syrupy. Cut vanilla bean length wise and scrape off the seeds over the dish to sprinkle them around. Peel, core, and cut apples into quarters. Place the quarters mostly sideways with rounded side tilting downward, in a very tight spiral pattern in the pan, starting with the rim. If making a temperature sensitive crust, cover with tin foil and bake the apples 25min, then remove and carefully add the crust (or wait until cooler), tucking in the edges with a spoon so as to not burn yourself. Pierce with fork and bake another 35. If making the almond flour crust, place chilled crust on top of uncooked apples, tuck it in all around, prick with fork, loosely cover with foil, and bake 55min. Cool 10min then run knife around edge and invert onto a large plate. Don't wait too long to invert or the caramel will stick to pan.