Melt the butter in a large pot over medium-high heat. Add the onions and cook, stirring occasionally, until the onions are golden and caramelized, about 10 minutes.
Add the garlic and cook, stirring, for 1 minute.
Add the flour and stir to coat the onions. Cook for 2 minutes, stirring constantly.
Add the beef broth and bring to a boil. Reduce the heat and simmer for 10 minutes.
Add the thyme and Worcestershire sauce and season with salt and pepper, to taste. Simmer for 5 minutes.
Garnish with parsley and serve hot.
Interesting Facts
This soup is a great way to use up stale bread, as it can be served with toasted slices of bread.
Onion soup is believed to have originated in ancient Rome.
It is a popular comfort food in many countries, including the United States.