For the potatoes:
- 3 large Russet potatoes, pricked all over with a fork
- 1 pound celery root, peeled and cut into cubes
- 4 tablespoons butter
- 2 egg yolks, plus 1 egg
- Celery salt
- Freshly grated nutmeg
- A splash of heavy cream
For the meatloaf:
- 6 tablespoons butter, divided
- 1 cup panko or homemade coarse breadcrumbs
- 1 teaspoon celery salt
- 1/4 cup parsley, finely chopped
- 1/2 cup cloudy apple cider
- 1/2 pound mushrooms, finely chopped
- 1 teaspoon fennel seed (1/3 palmful)
- 4 shallots or 1 small onion, finely chopped
- 2-3 small ribs celery and leafy tops, finely chopped
- 1 Honeycrisp, Jonagold or Braeburn apple, peeled and finely chopped
- 2 tablespoons thyme, finely chopped
- 2 tablespoons sage, thinly sliced
- 1/4 cup Calvados, brandy or dry sherry
- 2 pounds ground beef, pork and veal mix
- 1 cup roasted or jarred chestnuts, finely chopped (optional)
- 1 cup shredded sharp white cheddar cheese (1/4 pound)
- 1/4 cup grated Parmigiano Reggiano cheese
- 2 egg yolks
For the gravy:
- 4 tablespoons butter
- 1 teaspoon coarse black pepper
- 3 tablespoons flour
- 3 cups veal stock or beef stock
- 1 tablespoon Worcestershire sauce
For the potatoes, pre-heat the oven to 400°F. Roast the potatoes on a baking sheet for 1 hour and 15-20 minutes; let cool. Remove the potatoes from their skins and pass them through a ricer.
Bring a medium size saucepot of water to a boil. Salt the water and cook the celery root until very tender, 20 minutes. Drain and pass through a ricer; add to the potatoes. Combine with the butter and egg yolks; season with celery salt, pepper and nutmeg. Fit a pastry bag with a 3/4-inch star tip. Line a baking sheet with parchment paper, then pipe out 12 cones 2 1/2-inches wide and a couple inches high. Beat the egg with cream and lightly brush the cones.
For the meatloaf, melt 2 tablespoons butter over medium heat in a small skillet. Add the breadcrumbs, then season with celery salt and pepper and toast to golden. Remove from the heat and cool. Toss the toasted breadcrumbs with parsley and moisten them with apple cider. Set aside.
Melt 4 tablespoons butter over medium heat. Add the mushrooms and fennel seed; cook to brown lightly, then season with salt and pepper. Add the shallots, celery, apple, thyme and sage and cook to soften, 6-8 minutes more. Deglaze the pan with Calvados, brandy or sherry and remove from the heat to cool.
Season the meat with salt and pepper, then add the cooled mushroom mix, cooled breadcrumbs, cheeses and egg yolks and mix to combine. Form a loaf on a parchment-lined baking sheet and bake on a center rack at 375°F for 1 hour. Add the Duchess potatoes after 15 minutes and bake for 45 minutes, to crisp.
For the gravy, melt the butter over medium heat in saucepot; add the pepper and whisk in the flour. Bring to a bubble, then add the stock and simmer to thicken. Add the Worcestershire sauce, to taste.