In a large pot, heat the olive oil and butter over medium-high heat. Add the onions and cook, stirring occasionally, until they are softened and golden brown, about 8-10 minutes.
Add the flour and cook, stirring constantly, for 1 minute.
Slowly add the chicken broth and stir until the mixture is smooth. Bring to a boil, then reduce the heat to low and simmer for 10 minutes.
Stir in the heavy cream, thyme, salt, pepper, and nutmeg. Simmer for an additional 5 minutes.
Serve the soup warm, topped with croutons or shredded cheese, if desired.
Interesting Facts
Onion soup originated in France in the 18th century.
Onion soup is a popular dish in many countries around the world.
Onion soup is often served topped with croutons or shredded cheese.