What is the difference between a brunoise and a mirepoix?

--Sylvia

Both brunoise (pronounced "broon-WAHZ") and mirepoix (pronounced "meer-PWAH") are preparations of vegetables used in cooking. 

A mirepoix is a dice or rough chop of carrots, onions and celery used as a flavor base in cooking.  The dice is usually around 1/4 inch (6 mm) to a side, although it may be larger, for example when used as a base on which meat is roasted.  In that case, it may be as large as an inch (25 mm), or larger, in order to keep the meat well above the drippings that come out during roasting.  According to Larousse Gastronomique mirepoix was invented by the cook of the Duc de Lévis-Mirepoix.  When used for cooking meats, the mirepoix may also contain ham or bacon, both of which will add flavor to the dish.

A brunoise, on the other hand, is any vegetable cut to a fine dice, around 1/8 inch (3mm).  Brunoise can be made from the same ingredients as a mirepoix, or it may include other vegetables, such as turnip, parsnip, bell peppers or zucchini. 

Both mirepoix and brunoise are used to add flavor to braises.  Mirepoix is also typical as an ingredient in the preparation of stocks where the fine dice of a brunoise is unnecessary, and either can be used as a garnish.  They may also both be used as an ingredient for stuffings, where they are frequently sautéed beforehand.

Because of the similarity in applications the two are frequently confused, but the differences are in the size of dice, brunoise being a finer dice, and ingredients since a mirepoix is limited to the three vegetable mentioned.

A mirepoix is essentially the same as a soffritto in Italian cooking, or if you replace the carrots with diced bell peppers, you have the holy trinity used in cajun and creole cooking.