When you make onion soup in a slow cooker, the flavor becomes intense—especially when you cook it for 24 hours. First, you create the broth and leave it overnight in the slow cooker. The resulting beef stock is rich in vitamins and minerals including calcium, magnesium, and phosphorus. It promotes strong, healthy bones and is good for your digestion and immune system. In the morning, you add the rest of the ingredients and let everything simmer together all day on low heat. Your deeply flavored soup will be ready by dinnertime. Top each serving with crusty bread and a slice of cheese and broil until bubbly before digging in.

2 to 3 pounds grass-fed beef bones
3 carrots, coarsely chopped
3 celery stalks, coarsely chopped
1 large onion, coarsely chopped
2 bay leaves
5 garlic cloves
Fine sea salt
2 T. ghee
6 large yellow onions, sliced
2 T. all-purpose flour
1/2 C. dry white wine
8 slices crusty bread
8 slices Gruyere cheese

Preheat the oven to 350°F. Place the beef bones in a large roasting pan and cook them until well browned, about 30 minutes. Place the bones in the slow cooker. Deglaze the roasting pan with 1/4 C. hot water; use a wooden spoon to scrape off the parts that stick. Add this flavorful water to the slow’ cooker along with the carrots, celery’, onion, bay leaves, and garlic. Fill the slow’ cooker with water. Set the temperature to low’ and leave it overnight, about 12 hours. In the morning, strain the broth through a large colander, discarding any solid pieces. Turn off the heat and let the broth cool down. The stock will set like gelatin and the fat will rise to the top and harden. Skim the fat off. Taste the broth; season with salt to taste. Pour 10 C. stock back into the slow’ cooker. (Refrigerate the remaining stock in an airtight container for up to 4 days, or freeze for up to 6 months.) Melt the butter in a large sauté pan over medium heat. Add the onions and sauté, stirring frequently, until they brown, about 20 minutes. Add the flour to the onions. Cook, stirring with a wooden spoon, for about 1 minute. Deglaze the pan with the white wine. Add 1 T. salt and cook for 1 minute, then add the mixture to the slow cooker. With the slow’ cooker still on low, cook until the onions are very soft, about 8 hours. Before serving, preheat the oven to 400°F. Arrange bread slices in a single layer on a baking sheet and bake until crispy, about 10 minutes. Divide the soup between individual ovenproof bowls. Float a slice of the crispy bread in each soup bowl and top with a thick slice of Gruyere cheese. Set the oven to broil and broil until the cheese is golden brown, about 3 minutes. Serve hot.