Prep: 10 min., Cook: 1 hr. For an upscale single-serving option, ladle soup into ovenproof bowls. Top each bowl with a French bread slice and Swiss cheese slice. Place bowls on a jelly-roll pan, and broil 5 inches from heat until cheese is melted.
Melt butter in a large Dutch oven over medium-high heat. Add onions, and sauté 20 to 24 minutes or until onions begin to caramelize and are very tender. Sprinkle with 1 tablespoon flour, and stir gently. Remove from Dutch oven.
Toss beef in remaining 2 tablespoons flour. Cook beef in hot oil in Dutch oven over medium-high heat 6 to 8 minutes or until browned.
Add wine and broth, and stir to loosen particles from bottom of Dutch oven. Add onions and any accumulated juices to Dutch oven; bring to a boil. Cover, reduce heat to low, and simmer 30 minutes.
Meanwhile, preheat oven to 350°. Bake bread slices on a jelly-roll pan 8 to 10 minutes or until crispy and lightly toasted. Serve with soup.