Using a piece of kitchen twine, tie together the parsley, thyme, and bay leaf into a bundle.
In a large non-reactive bowl, combine the onions, pork, beef, lamb, carrots, ham hocks, garlic, and herb bundle. Pour in the wine, stir to combine, and let marinate in the refrigerator for 24 hours.
Preheat the oven to 325 degrees F.
Butter the inside of the baking dish. Strain then separate the meat and vegetables; reserve the wine.
In the baking dish, layer half of the vegetables, potatoes, leeks and all the meat, seasoning each layer with salt and pepper, to taste. Repeat with the remaining vegetables, potatoes, and leeks. Pour over the reserved wine from marinade. Dot the top with the 6 tablespoons of butter.
Cover the baking dish with the lid. Roll the bread dough, if using, into a rope the circumference of the baking dish. Press the dough rope around the edge of the lid, pressing it slightly to seal. Brush the bread with some of the beaten egg. Bake for 2 1/2 hours.
Remove the bread, uncover, and serve immediately.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Jean Luc Kiefer, Park Bistro, NYC, NY