Linked from
The 9 pages that link to Mirepoix, each with the reason it gives.
CeleryRelated: Celery supplies one of the three classic aromatics in this mixture.
LeekRelated: Leek can replace or supplement onion in aromatic bases for soups and stews.
Chicken soupRelated: These vegetables commonly flavor the broth as it simmers.
Shepherd’s pieRelated: These aromatic vegetables commonly build flavor in the lamb filling.