Preheat oven to 350 Degrees
Put your fruit in a small saucepan and place it on the stove on low, 1-2. Let it come to a simmer while you prepare your pastry dough but watch it and stir it occasionally to break down the fruit.
Combine your flour, salt, sugar, cinnamon, and nutmeg in a mixing bowl and whisk well. Using a pastry cutter blend in the butter (or chilled olive oil if keeping it vegan). The dough will be crumbly but dry.
Separate the egg and keep the whites for a brush over your pastry later. Add the yolk to the 4 tablespoons of kefir or milk substitute you are using to bring the dough into a formable pastry dough. If it looks dry, use the 5th tablespoon of milk. You can chill it for an hour if you like, then roll it out.
Check on your fruit filling, it should be heated and ready to purée in a blender or food processor. The fruit should have enough liquid present, so you don't have to add water, that is why you are heating it very low. But some fruit with low water content, like blueberries may need a little (say 2 Tbsp.) water added. Use your best judgment without letting it burn. Once it is pureed, place it back on the stove and add the maple syrup or honey. It will still be too thin and watery, so add the tapioca starch and stir until the fruit thickens to a thick paste. Remove from heat and add vanilla, stir well and set aside until it cools and you work on your dough. Preheat oven to 350 Degrees
Get your chilled dough out and place a large piece of parchment paper on the counter and another over the ball of dough. Roll the dough out thinly and evenly between the paper, then peel off the top layer of paper and cut off the outer edges. Form a square of the dough, then cut dough into small rectangles (about 2.5 inches by 3 inches). Use a fork to place small holes in the dough.
Once you have your dough pieces cut place it on the parchment paper, hole sides down on a baking sheet. Spread a teaspoon or so of the fruit filling on the inside of the square, leaving about a 1/4 of an inch unfilled dough around the edges.
Place the second piece of dough over the filling on your bottom square evenly and press the edges together with a fork. Brush with the egg whites and bake at 350 degrees for about 18-20 minutes or until golden brown.