Heat 2 Tbs. butter in a skillet over medium-low heat until it bubbles. Add the onion, garlic, and pear or apple and cook slowly, while stirring, until soft. Spoon the pan contents into a food processor bowl.
Heat 1 Tbs. butter in the skillet. Raise the heat to medium-high and add the livers. Season with salt and pepper. Cook until seared all over. (They should remain a little pink in the center.)
Lower the heat and add the Cognac or Calvados. If you feel comfortable about flaming things on the stove, touch a flame to the mixture and burn off the brandy until the flames stop. (Otherwise, just let the brandy boil away until only a little liquid remains.)
Add the livers to the food processor. Run the processor until the mixture is completely smooth. If it gets thick, add a little cream to loosen it up.
Cut the stick of butter into about ten pats, and add them three at a time to the mixture, processing until they disappear. Adjust salt and pepper to taste.
With a rubber spatula, remove the pate to ramekins. Cover with small pieces of waxed paper and refrigerate for at least three hours. It's best to remove the pate from the refrigerator about an hour before you serve it.
