In a large pot over medium heat, heat oil. Whisk in flour and cook until it turns a dark brown color. Add onions, celery, bell pepper and garlic and cook until softened.
Add bay leaves, thyme, tomato paste and chicken broth or stock. Bring to a boil then reduce heat to low. Simmer for 1 hour.
Stir occasionally and season with salt and pepper to taste before serving.