Elizabeth Taylor's Chicken with Avocado and Mushrooms

1 dark-skinned California avocado (Haas), peeled and cubed
1 tablespoon lemon juice
2 (2 1/2 pound) chickens, cut into serving pieces
Salt and freshly ground pepper
1/4 cup butter

Sauce
3 finely chopped shallots
3 tablespoons cognac
1/3 cup dry white wine
1 cup whipping cream
2 cups sliced fresh mushrooms
3 tablespoons butter
1 cup chicken stock
Chopped fresh parsley, for garnish

Sprinkle avocado with lemon juice. Cover and refrigerate.

Season chicken with salt and pepper.

In a large heavy skillet, over low heat, heat 3 to 4 tablespoons butter and saut