Goose Liver Terrines

Name: Goose Liver Terrines
Ingredients: 12 tbsp. unsalted butter; 1 shallot, minced; 1 clove garlic, minced; ½ cup chicken stock; 3 sprigs thyme, stems removed; 1 lb. goose livers, cleaned (see The Whole Goose); ½ cup heavy cream; Kosher salt, to taste; 3 ½ tsp. powdered gelatin; 3 cups Concord grape juice; Whole-grain mustard and rye crackers, for serving