Preheat the oven to 325 degrees F.
In a small pot, combine the prunes and wine and bring to a simmer over medium heat. Cook gently until the wine clings to the prunes, 7 to 10 minutes. Remove from the heat and let cool to room temperature.
Place the hazelnuts on a baking sheet and toast until dark golden brown, 15 to 20 minutes. Transfer the nuts to a clean kitchen towel, gather up the sides to make a pouch, and roll them on the counter to rub off the skins. Unfurl the cloth, and roll the nuts to the edge and into a dish. When the nuts are cool, crush them to a medium grade, using a knife, a mortar and pestle, or a small food processor.
Heat a medium skillet over medium heat and add 3 tablespoons of the butter, the onions, and 1/2 teaspoon of the salt. Cook uncovered, stirring often, until dark golden and sweet, about 20 minutes. Scrape onto a plate to cool.
Bring a 2-quart saucepot of well-salted water to a boil.
Blanch the cabbage leaves in the boiling water until wilted, about 1 minute each. Run the leaves under cold water to cool; shake off excess water. Cut away the thickest part of the stems. Dry the leaves and set them aside on a plate until ready to use.
Raise the oven temperature to 350 degrees F.
In a large bowl, combine the pork, breadcrumbs, parsnip, carrot, parsley, thyme, sage, pepper, nutmeg, eggs, the cooled onions, and the remaining 1 1/4 teaspoons salt. Mix swiftly with your hands until just combined.
Pile the meatloaf mixture into the center of a 9-by-13-inch baking pan and pat into a long rectangular shape. Press the prunes 1/2-inch deep into the meat, like buttons running down the center of the loaf. Pull some of the meat off of each end and use it to cover the tops of the prunes.
Cover the meatloaf with overlapping cabbage leaves. Rub the outside of the leaves with the remaining 2 tablespoons butter.
Bake until the internal temperature reaches 160 degrees F on an instant-read thermometer, 50 minutes to 1 hour.