Chop the chestnuts.
Cook the bacon in three tablespoons unsalted butter in a heavy saucepan over medium heat, stirring until the bacon is crisp on the edges, about five minutes.
Add the onion and garlic and continue to cook, stirring, until the onion is softened.
Add the chestnuts and water. Simmer, stirring, until the liquid is reduced by about half. Discard the smashed garlic.
Transfer the mixture to a bowl and mash to a coarse paste with a fork.
Peel half of the apple. Cut the peeled half into ¼ inch pieces until you have enough to measure three tablespoons. Reserve the remaining unpeeled apple.
Stir the diced, peeled apple into the chestnut mixture with the Parmesan cheese, the parsley, and the salt and pepper to taste.
Put one won ton wrapper on a work surface, being careful to keep the remaining wrappers covered in plastic wrap so they don't dry out.
Mount a scant tablespoon of the chestnut filling in the center of the wrapper and lightly brush the edges with water. Top with a second wrapper, pressing down around the filling to force out the air.
Trim the excess dough off with a 2¾ inch round cookie cutter and seal the edges well, pressing them firmly with your fingertips.
Transfer the ravioli to a dry kitchen towel, then make more in the same manner.
Cut enough of the unpeeled apple into a ¼ inch dice until you have three tablespoons, and toss with the lemon juice.
Heat the remaining 4 tablespoons of butter in a large heavy skillet over medium heat until the foam subsides and the butter begins to brown.
Stir in the sage and cook, stirring, until the sage is crisp and the butter is golden brown. Season with salt and pepper.
Add the ravioli to a 6 quart pot of salted boiling water, then cook at a slow boil, stirring gently from time to time, until the pasta is tender 3 to 5 minutes.
Carefully transfer the ravioli with a slotted spoon to a colander to drain.
Slide the ravioli into the sage butter and cook over moderate heat, stirring gently, for 1 minute.
Sprinkle the ravioli with the unpeeled apple and season with pepper.