Preheat the oven to 350 and butter the ramekins.
Peel and core all the apples. Then thinly slice them on a mandolin.
Melt the butter. In a small bowl, combine melted butter, lemon juice, lemon zest, cinnamon, sugar, nutmeg and salt.
Dip each apple slice in the butter mixture and then layer into a ramekin. Repeat this process until the layers reach almost to the top (about 40 layers). Flip each ramekin over into the bowl to drain out the excess liquid.
Bake the apple pies (without the crust) for 10 minutes.
While the pies bake, roll out the puff pastry and cut out circles that are roughly the size of your ramekins.
After their 10 minute bake, carefully top each ramekin with a circle of puff pastry. Return to the oven and bake until pastry is golden brown, 20 minutes.
Allow the pies to cool and serve with ice cream or whipped cream. You can also flip them upside down out of the ramekin to serve if you'd like.