Makes one 4x4x9''/10x10x23cm pullman loaf pan, or 3x4x11''/7.5x10x28cm. Make 3 to 4 Days Ahead. Originally folding loaf pans are used to make pâtés en croûte because they can be removed from the mold without the risk of damaging it.
Place the softened butter in the bowl of a stand mixer fitted with the paddle attachment and cream with salt and sugar on medium-high speed, then add cornstarch and mix until homogenized on low speed. Pour in the egg, water and white vinegar and mix until smooth on medium speed. Mix in one-third of the flour and add remaining flour on low speed. Wrap up and refrigerate until firm or overnight and leave dough 15 minutes on the counter before using. Dust work surface with flour or cornstarch and work dough until just pliable. Roll into a large 15''x19''/38x48cm and 0.15''/4mm rectangle. Fit the dough into the greased mold (grease mold generously with cooking spray) and gently work it to fit snugly. A ball of dough dipped in flour helps. Fit the dough into the corners without tearing leaving the dough overhang by 1/2''/2.5cm or more so you can seal the dough cover on the outer edge later. Chill the loaf pan along with remaining dough for 2 hours or more.
*Pink curing salt (sodium nitrate) helps both to prevent the growth of bacteria and to preserve the original color of the meat. Vitamin C acts as an antioxidant, which means it keeps foods from reacting with oxygen when they're exposed to air. This helps keep the food's texture, flavor, and color from changing. Divide pork shoulder, belly and chicken breast into cubes and mix meats into the port and brandy marinade. Gently, remove membrane from the chicken livers and mix into the pink salt marinade. Cover with plastic wrap in contact and place meats in the refrigerator to marinate for 24 to 48 hours. When marinating time is over, sear chicken livers quickly with some fat on high heat for a minute, let cool and set aside.
Cook mushrooms for 5 minutes with 1 teaspoon/5ml olive oil and butter, 1/2 lemon juice, 1 tablespoon/15ml water, a thyme sprig, a bay leaf, salt and pepper. Drain and let cool. Beat eggs with salt and pepper, shallots and parsley. Mix in the marinated meats with the exception of livers and mushrooms.
Fill the mold with the forcemeat alternating with the cooked mushrooms and seared chicken livers and its rendered juice. For the top crust or cap, roll out remaining pastry into a 11''x6''/28x15cm rectangle. Lightly use egg wash or water to “glue” the pastry together in the corners and pinch the seams. You can also fold the liner and then the excess dough over the top of the forcemeat. Pinch the edges of the overlapping dough slightly so that when the dough is overlapped, it has the same thickness as the other three sides. Allow loaf to rest an hour in the refrigerator. Trim and score borders. Brush top twice with egg wash and lightly score the top of the loaf with the back of a paring knife. Make 2 chimneys using a round pastry tip and place one tube in each hole or insert a cylinder of rolled aluminum foil. Chimneys allow the escape of steam and to prevent melted fat from bubbling over the top crust as the pâté bakes.
Soak gelatin in cold water to soften; drain. Bring to boil water, port and salt. Turn off the heat, and mix in gelatin; reserve.
Set the oven rack adjusted to the bottom position and preheat with a baking sheet or a pizza stone; this will ensure the bottom crust to cook through. Bake at 350ºF/180ºC for 1 hour and 30 minutes or until an inserted thermometer in the center reads 155ºF/68ºC. Lower temperature to 325ºF/160ºC if using a convection oven). Remove loaf from the oven and let cool completely to 100ºF/38ºC and slowly pour the warm aspic port through both chimneys and refrigerate overnight. Add more aspic if need and chill again. Carefully remove the mold by heating up the bottom over the flame a few seconds to ease the process (no need to do that if using a folding loaf pan). Wrap up, and refrigerate for up to a week.
Slice pâté with a serrated knife. Serve with pickles and bread (Look recipes up). Enjoy!