Place the butter, onion, apple, thyme, and salt into a 3-quart saucier and set over medium heat. Stir to combine. Cover and cook until the apples and onions are softened and are just beginning to brown, about 5 minutes.
Remove the lid, add the livers, and cook until firm but still pink inside, approximately 5 minutes. Add the pepper and brandy and simmer for 1 minute. Remove from the heat and cool for 5 minutes. Transfer the mixture to the bowl of a food processor and process until smooth, approximately 1 minute. Pour the mixture into a medium mixing bowl, cover, and place in the refrigerator until chilled, approximately 1 hour.
Place the heavy cream into a medium mixing bowl and whisk until soft peaks form. Fold the heavy cream into the liver mixture in thirds. Serve chilled.