Preheat the oven to 160°C (325°F). Tear the crust from the Country Bread into pieces and soak it in the Whole Milk until softened, about 10 minutes; then squeeze out excess milk and set the soaked bread aside.
Trim and cut the Pork Shoulder, Pork Back Fat and Pork Liver into 2–3 cm pieces suitable for grinding or very fine chopping. If you prefer a smoother terrine, pass them through a coarse and then a fine grinder; for a rustic texture, pulse in a food processor until evenly minced.
Finely chop the Shallot, crush the Garlic and sweat both gently in a little oil over medium heat until soft and translucent; cool before adding to the meat mixture.
Place the minced meats in a large bowl with the squeezed bread, the cooled shallot and garlic, chopped Flat-Leaf Parsley, the beaten Egg, and the Thyme Leaves. Add a generous pinch of Sea Salt, freshly ground Black Pepper and a small amount (start with 1/2 teaspoon) of Quatre Épices; mix thoroughly until the mixture is well combined and slightly sticky.
Pour a splash of Cognac over the mixture and add one aromatic Bay Leaf to a small pan with a tablespoon of the cognac and warm briefly to release its fragrance; remove and discard the leaf, then pour the infused cognac into the meat and mix again.
Taste by frying a small patty in a skillet, then adjust seasoning with more salt, pepper or quatre épices as needed.
Line a terrine mold or small loaf pan with overlapping sheets of Pork Caul Fat, leaving enough to fold over the top. Pack the meat mixture firmly into the lined mold, pressing out any air pockets. Fold the caul fat over to seal and press a piece of parchment or foil on top to keep the surface smooth.
Place the terrine in a roasting pan and pour in hot water to come halfway up the sides of the mold. Bake in the preheated oven until the center reaches about 70°C (160°F), roughly 1½–2 hours depending on size. Remove from the water bath, weigh the terrine with a press or cans to compact it slightly, then cool to room temperature before refrigerating overnight to develop flavor and firm the texture.
When ready to serve, unmold and slice the terrine. Accompany with crisp Cornichons, coarse Dijon Mustard and slices of toasted Baguette. Store leftovers tightly wrapped in the refrigerator for up to 5 days.
