The casserole is sealed with a flour-and-water dough to prevent the wine from evaporating during the long cooking process.
In a large bowl, combine feet, tails, lamb, pork, beef, 3 1/2 cups wine, chopped onion, halved garlic, and ground pepper. Cover with plastic wrap, and chill overnight.
Preheat oven to 300 degrees. Place marinated meat mixture in a large saucepan. Bring to a boil; skim surface, and discard foam that rises to the top. Prepare a bouquet garni: Tie parsley stems, bay leaf, and thyme together with kitchen twine; set aside.
Coat a 5-quart covered casserole or Dutch oven with lard. Season potatoes with salt and pepper. Line the bottom of the casserole with half the potatoes. Top with half the sliced onions and half the leeks. Remove meat from marinade, and transfer to casserole. Strain marinade over meat, discarding solids. Top with remaining onion and leek, minced garlic, and bouquet garni. Distribute remaining 1 pound potatoes evenly in casserole. Pour remaining 3 cups wine over potatoes. Cover casserole.
Make the seal: In a medium bowl, combine flour and 1/2 cup warm water. Stir until mixture comes together and forms a dough. Roll dough into a log long enough to go around the casserole. Place dough over the seam between the casserole and the cover to seal. Brush dough with egg. Bake for 3 hours. Remove dough seal, and serve immediately.