Any muscle meat you get from an older animal will have a stronger flavor than the same cut from a younger animal. The same guideline goes for offal cuts, such as beef liver, but to a greater degree. Beef liver, whether from a calf or an ox, has a metallic flavor and toughness that increases with the age of the animal. Pureeing beef liver into a paste, or pate, takes tenderness out of the equation and provides the several options for embellishing its flavor with seasonings, giving you a much more palatable dish than if you sauteed or roasted it.
Trim any connective tissue, fat and visible veins from the beef liver. Soak the liver overnight in buttermilk, or for at least eight hours.
Saute the base aromatics for the pate in a few tablespoons of oil until fragrant, about four or five minutes. Base aromatics comprise garlic and shallots, onions or leeks.
Place the aromatics in the refrigerator and chill them for about 30 minutes. Chill the food-processor bowl in the freezer for about 20 to 30 minutes.
Rinse the liver while rubbing your fingers over it vigorously. Pat the liver dry with paper towels.
Dice the beef liver into 1-inch pieces.
Add the diced beef liver and an equal amount of rendered animal fat to the food processor. Animal fats, such as schmaltz, pork fat or duck fat, are the traditional fats used in pate.
Add an equal part of lean ground meat to add body to the pate and dilute the metallic taste of the beef liver. Hard-boiled eggs, turkey, ground pork loin or ground chicken are the lean meats classically used to add body and secondary flavor to pate.
Add fresh herbs and seasonings to the beef-liver pate. This is the point you let your palate guide you in adding seasonings that take away from the metallic taste. Aggressive seasonings, such as paprika and chili powder, play well off the acrid taste, and give you latitude when it comes to spiciness.
Add an acid to the pate. Acids, like bold spices, takes away from the metallic flavor of beef liver and tilt the balance in favor of savory. They also contrast with the fat. Lemon juice, flavored vinegar, soy sauce or spicy mustard all work well
Add a teaspoon or two of Cognac or brandy to the pate. Cognac and its substitution, brandy, are used for flavoring only, so they're optional. They are important, though, if you're going for a classic flavor.
Season the pate to taste with kosher salt and freshly ground black pepper. Use about 1 teaspoon of each for every pound of beef liver and lean meat as a guideline since you can't season to taste yet.
Pour about a tablespoon of cream in the food processor and pulse the beef liver several times. Run the processor at high speed and add cream, 1 tablespoon at a time, just until the ingredients homogenize.
Take a large spoonful of pate from the processor and check its consistency. It should have the consistency of a dense paste, and have a coarse texture and uniform color.
Hold the spoon upside down. The pate should stick to the spoon for several seconds. If the pate falls off the spoon in pieces, process in a whole egg or panada, a mixture of white bread soaked in milk and whole eggs, to bind it.
Spoon the pate into a loaf pan or a terrine pan lined with a larger piece of parchment paper. Smooth the top of the pate with the back of a spoon and fold the paper that hangs over the sides of the mold over the pate. Tamp the pate down lightly with your fingers.
Cover the mold with a couple layers of aluminum foil. Place the pate in the refrigerator for at least two hours to let the flavors blend.
Heat the oven to 350 degrees Fahrenheit. Place the pate in a deep oven dish and add enough water to reach about three quarters up the sides of the mold.
Bake the beef-liver pate until it reaches a minimum internal temperature of 165 F. Check the temperature after about two hours by inserting a meat thermometer through the foil into the center of pate.
Place the pate on a trivet after you take it out of the oven and let it rest for 45 minutes to an hour. Chill the pate in the refrigerator until cold and firm, about two hours.