Preheat oven to 375°F. Line a baking sheet with parchment paper and set aside.
Add the butter, apples, sugar, lemon juice, vanilla, cinnamon, allspice, nutmeg, walnuts, and water to a saute pan on medium heat. Bring to a simmer until the liquid turns to a syrup then remove from the heat and let cool.
Place the pastry onto the baking sheet and roll it out slightly, using a rolling pin to thin it out a little bit (this will help cut down on cooking time). Optional: make slices about 1 inch thick on both sides of the puff pastry to make a lattice top.
Spread the apple mixture evenly down the center of the pastry lengthwise.
Fold the sides of the pastry around the apples. Lightly brush the top with butter and sprinkle with cinnamon and sugar.
Bake for about 25 minutes, until golden brown.
Let cool before slicing, Serve cool or reheat to serve warm.