Pre-heat oven to 450°F.
Cut an X into the round end of each chestnut, and place on a baking sheet. Transfer the baking sheet to the oven and pour ¼ cup of water onto the sheet.
Roast the chestnuts for 10 minutes, until the shells are starting to peel back from the cut lines. Remove the baking sheet from the oven and let cool for a few minutes.
Peel the chestnuts while they are still warm and chop coarsely.
Reduce the heat of the oven to 350°F and butter an 11"x7"x2" baking dish.
In a large skillet over medium heat, sauté the pancetta until crisp, about 10 minutes.
Using a slotted spoon, move the cooked pancetta pieces to a plate lined with paper towel and set aside.
In the same skillet, melt ¾ cup of butter over medium-high heat and add in the onion, celery, garlic, chopped rosemary and sage. Sauté until the onions are soft, about 8 minutes.
Transfer the onion mixture to a large mixing bowl. Add in the cubed cornbread and Ciabatta bread, the chopped parsley, the roasted chestnut pieces and the cooked pancetta. Toss together and pour in the chicken stock a bit at a time until the stuffing is moist. Mix in the eggs and season with the Kosher salt and black pepper.
Spoon the stuffing into the buttered baking dish, cover with tin foil, and bake for 30 minutes. Uncover and continue baking another 20-30 minutes until the top is golden brown.