If you are drying your own apples: Position racks in the upper and lower thirds of the oven and preheat to 200° F. Slice the apple very thinly--using a mandolin helps for this. I don’t bother to core the apple as the seeds just fall out as you slice. Place the apple slices on a parchment lined sheet pan and bake for 1 hour. Turn the apple slices over and rotate the pans. Bake for another hour. Test the slices to see if they are crisp. If so, remove them from the oven and let the apples cool completely before removing them from the pan. If not, bake the apple slices for an additional 15-20 minutes, or until completely dry and crisp. These will keep for several weeks in an airtight container.
To bake the granola, preheat the oven to 300° F.
Split the vanilla bean in half lengthwise and scrape out the seeds with a paring knife. Place the sugar in a small bowl and add the vanilla seeds. Using your fingers, rub the seeds into the sugar; this will keep the vanilla from clumping together in the granola.
Place the vanilla sugar in a large bowl. Add all the dry ingredients (not the dried apple slices) and stir to combine thoroughly.
Combine the wet ingredients in a medium bowl and whisk well to combine. Pour the wet ingredients over the dry ingredients and stir until all the dry ingredients have been coated.
Divide the granola between two parchment-lined sheet pans. Spread the granola out and place the pans in the oven. Bake for 45 minutes, rotating the pans and stirring the granola every 10 minutes or so. After 45 minutes the granola will be golden but not completely dry. Don’t worry about that, it will crisp up as it sits. Place the sheet pans on wire cooling racks and give the granola a final stir so it doesn’t dry into big clumps.
When the granola is completely cool, stir in the dried apple slices. Transfer it to an airtight container (I like a big mason jar) and store in a cool dry place. Tightly covered, the granola will keep for several weeks.