Special equipment: butcher's twine
For the stuffing and pork: Preheat the oven to 350 degrees F.
Coat a large saute pan with olive oil and heat through. Add the sausage and cook until brown, breaking it up into pieces with the back of a spoon, about 5 minutes. Add the onions, sprinkle with salt and cook until the onions are softened and slightly brown, about 2 minutes. Add a few tablespoons of the chicken stock if needed to help deglaze the pan. Stir in the sage and apples, and continue to cook for an additional minute. Remove from the heat and transfer to a mixing bowl to cool.
While the filling cools down, carefully slice through the pork chops to open the thickest part like a book. Place each pork chop in between plastic wrap and pound lightly with the toothy side of a meat mallet, then the smooth side, to flatten and even out the pork. Set aside.
Stir the breadcrumbs, Parmesan, 1/4 cup of the chicken stock and the eggs into the sausage mixture. Adjust the seasoning if needed.
Lay one of the pieces of caul fat out on a large, flat work surface. Lay 3 to 4 slices of prosciutto in the middle in a single layer. Arrange one pork chop on top. Lay some of the stuffing mix on the pork and roll it up, creating a neat even log. Wrap the caul fat in an even layer around the pork log, being sure to wrap around the open ends, to create a smooth even log. Tie with butcher's twine to secure. Repeat with the additional caul, prosciutto, pork and stuffing.
In a large saute pan, coat the bottom of the pan with olive oil. Bring up to medium-high heat. Place one of the involtini into the pan and sear until brown on all sides. Remove from the pan, blot on paper towels and transfer to a baking sheet. Cook the second in the same manner (be sure to keep the saute pan for the sauce). Put the involtini in the oven and bake until cooked through, 5 to 7 minutes.
For the pan sauce: While the involtini are baking, add a few drops of chicken stock to deglaze the saute pan from the seared meat. Add the apples and shallots, sprinkle with salt and cook for 3 to 4 minutes. Remove the pan from the heat, add the apple brandy and then set it over medium-high heat. Reduce the brandy by half. Add half the chicken stock and the sage, season with salt and bring it to a boil. When the stock has reduced by half, add the remaining stock and reduce by half again. Remove the sage leaf and stir in the butter. Taste and adjust the seasoning if needed.
Allow the meat to rest before slicing. Serve with the pan sauce and garnish with sliced chives.