1 dash hot pepper sauce (such as Tabasco®), or to taste
•
4 thick slices French bread
•
basil and garlic-flavored olive oil for brushing
•
2 cups grated Gruyere cheese
Instructions
Place water, beef ribs, parsnips, onions, carrots, celery, bay leaves, 1 teaspoon salt, 1 teaspoon black pepper, and 1 tablespoon fresh thyme into a large soup pot over medium heat; bring to a boil. Reduce heat to a simmer and cook, skimming and discarding foam that forms on top of broth, until broth is a rich brown color, 5 to 6 hours. (Broth may also be made in a slow cooker.) Strain broth, discard ribs and vegetables, and refrigerate extra broth.
Melt butter in a large heavy skillet or cast iron pan over medium-low heat. Cook onions and garlic until caramelized and brown, about 30 minutes.
Mix flour, herbes de Provence, paprika, and garlic powder together in a bowl; sprinkle over browned onions. Cook and stir 5 minutes; season with salt and black pepper. Stir in parsley and 1 teaspoon thyme.
Pour in 4 cups beef broth, white wine, sherry, and hot pepper sauce; simmer until flavors have blended and soup has thickened, about 15 minutes. (More time doesn't hurt.)
Preheat the oven broiler about 15 minutes before serving time. Place a rack about 6 inches from the heat source.
Brush slices of French bread with flavored olive oil. Toast under the preheated broiler until well-browned on each side, 1 to 2 minutes per side. Ladle soup into oven-proof soup bowls; place a toasted bread slice on top of each bowl. Sprinkle each bread slice evenly with Gruyère cheese.
Place the filled soup bowls under the broiler until cheese is melted, bubbly, and browned, 2 to 4 minutes.