Mirepoix (diced root vegetables) is diced roasted vegetables used as a seasoning ingredient for sauces and meat dishes. Cut vegetables and bacon into tiny cubes, add a little bit of thyme and bay leaf, lightly roast with a little bit of butter, pour off the fat and pour the mirepoix (diced root vegetables) into the simmering sauce.
The Duke of Mirepoix (diced root vegetables) (1699-1757) gave his name to this sauce seasoning.