Pasta dough: 1/3 chestnut flour and 2/3 white flour; figure the usual number of eggs.
Coarsely chop chestnuts.
Cook pancetta in 3 tablespoons butter in a large heavy saucepan over moderate heat, stirring, until crisp on edges, about 5 minutes. Add onion and garlic and cook, stirring, until onion is softened. Add chestnuts and water and simmer, stirring, until liquid is reduced by half. Discard garlic.
Transfer mixture to a bowl and mash to a coarse paste with a fork. Peel half of apple and cut enough of peeled half into 1/4-inch dice to measure 3 tablespoons. Reserve remaining (unpeeled) apple. Stir diced peeled apple into chestnut mixture with parmesan, parsley, and salt and pepper to taste.
Put 1 won ton wrapper on a work surface, keeping remaining wrappers in plastic wrap, and mound 1 scant tablespoon of filling in center. Lightly brush edges of wrapper with water and top with a second wrapper, pressing down around filling to force out air. Trim excess dough with cutter and seal edges well, pressing them together with your fingertips. Transfer ravioli to a dry kitchen towel, then make more in same manner.