Sauté onion, bacon, carrot and celery in oil until slightly browned.

Stir in flour; cook until flour is brown. Slowly add water stirring to obtain a smooth consistency.

Add tomato paste, stock cubes and bouquet garni sachet. Simmer sauce very slowly for 2 hours stirring occasionally.

Remove bouquet garni and blend or sieve through a strainer. Return sauce to pan and boil to reduce quantity if a very thick sauce is needed.