This soup is so rich and flavorful and packed with darkly caramelized onions that no one would ever imagine it was made in a slow cooker. The secret is roasting the beef bones for beefy flavor.unknown source
1Arrange beef bones on paper towel lined plate and microwave in batches, til well browned, 8 to 10 minutes.
2Add onions, butter, 1 tsp. salt, 1 tsp. pepper, sugar and thyme to slow cooker. Whisk flour, apple butter, sherry and soy sauce together in bowl til smooth, then stir into slow cooker. Nestle microwaved bones into slow cooker. Cover and cook til onions are softened and deep golden brown, 8 to 12 hours on high.
3Discard beef bones. Bring chicken broth and beef broth to boil in covered pan over high heat, then stir into slow cooker. Let soup sit til heated through, about 5 minutes. Season with salt and pepper to taste.
Just before serving, position oven rack 6 inches from broiler element and heat broiler. Lay bread on baking sheet and broil til golden on both sides, about 2 minutes per side. Sprinkle cheese over one side of bread and continue to broil til melted and bubble, 3 to 5 minutes. Ladle soup into serving bowl and top with broiled cheese bread.