Mirepoix vegetables are an essential part of French cuisine. Mirepoix is a combination of finely chopped onions, carrots and celery, with a proportion of 50% onions, 25% celery and 25% carrots, which is used to add aroma and flavor to soups, stocks and other foods. They are typically sauteed with butter before the other ingredients are added, and herbs and cubed meats may be included with the mirepoix. But mirepoix may also be added once the dish is finished, in order to refresh its flavors.
Vegetables for mirepoix must be finely chopped, since this allows the vegetables' flavor and aroma to be quickly released into the food. Depending on what food the mirepoix will be used with, the vegetables can be chopped as coarsely as one to two inches or as finely as 1/2-inch. However, it is very important that the pieces be as uniform as possible so that they will be cooked evenly. Many chefs also prepare the mirepoix vegetables in advance of when they will actually be used, and then store them in the freezer since they can stay fresh for several days after they've been chopped.
Chef Knife
Preparing onions and carrots for mirepoix involves a cutting technique called brunoise, which involves chopping them into very small pieces. To chop carrots for mirepoix, cut the four sides and the tip to make the vegetable into a roughly rectangular shape. Then cut them into very thin, even slices (a technique called julienne). Hold the slices together, then turn the carrot ninety-degrees and start dicing it into tiny squares. For onions, peel a bulb and then cut it in half, slice off the top and place the flat side down on the cutting board. Then cut it into thin slices. Make two horizontal slices which divide the onion roughly into threes, making sure to leave a little allowance at one end to help keep the onion together while it's being sliced. Then dice the onion by making vertical cuts.
Cutting celery for mirepoix vegetables is a similar process to cutting carrots. Prepare the celery stalk by removing the top and bottom part. Then make long lengthwise cuts across the stalk by placing the tip of the knife into the stalk and slicing downwards to create thin matchsticks. Then start dicing the celery. When you're first dicing vegetables for mirepoix, start by using manageable sizes since making the brunoise cuts can be tricky, then slowly move up to bigger ones.