Clean the chicken livers carefully, cutting away any green or brown spots, then wash them quickly under cold running water and pat them dry with paper towels. Now cut them in half.
In a large heavy frying pan, melt the first 3 T butter. Add the onions and shallots and cook over moderate heat for 5 to 7 minutes, stirring occasionally, until the onions and soft and lightly colored. M ix in the chopped apple and cook 3 or 4 minutes longer. When soft enough to mash with a spoon, transfer to the bowl of a food processor.
In the same pan, melt the second 3 T butter, this time over rather high heat. As the butter foam subsides, add the livers. Over high heat, turn them in the sputtering butter with a wooden spoon for about 3 or 4 minutes. When the livers are quite brown on the wutdiesa and still pink within, remove the pan fro the heat and flame them with the Calvados, which you have warmed slightly. Let the alcohot burn itself out completely.
Now add the livers and all their juices to the onion-apple mixture. Moisten with 2 T cream and process. Add more cream if necessary. Process until very smooth. With a rubber spatula, crape the mixture out into a fine mest sieve set over a mixing bowl. Rub the past through the sieve with the back of a spoon. Let mixture cool completely.
Cream the remaining 10 T of butter. When creamed, beat the cool liver paste, little by little into the butter. Stir in the teaspoon of lemon juice and the salt and pepper. Don't be sparing with the salt, since chilling deadens flavor, the pate will be surprisingly less salty than you thought.
Pack the pate into small terrines or any attravtive quart-size container. Smooth the top witha spatula and pour over it enough clarified butter to cover it completely. This will not only prevent the pate from changing color as it chills, but will make an almost airtight covering that lessens the possibility of spoilage. (If you do not use the clarified butter, cover the crocks with plastic wrap.) Refrigerate at least 3 hours.