In a classical French kitchen, brunoise refers to tiny dice of vegetables, prepared as a basis for soups and stocks, as well as a fiddly garnish for certain dishes as well.
Brunoise, (pronounced in rugged kitchenese as "Brun-Wahz") is the bane of many a young trainee chef, as it is one of the first tasks assigned to the young hopefuls. Quite often, a novice chef will spend a large amount of painstaking effort to ensure the dice of vegetables are breathtakingly small and uniform in size, only to have an over-zealous sous chef scream "Start over!" due to one or two pieces being different in size.
There really is no need to get so anal over this fairly important kitchen technique. The idea is to maximize the surface area so the most flavour possible is released within a short amount of cooking time. This makes it perfect for quickly prepared soups, stocks and sauces. Brunoise can refer to any vegetable cut into match-head size, but it generally means the troika of onion, carrot and celery, much the same as the Italian soffrito, apart from the addition of sage in Italy.
Brunoise is a useful technique to hone up your knife skills, so using the familiar basis of onion, carrot and celery, here is a rough guide on how to do it. Firstly, you will need a good sharp knife. Start with the onion. Cut the onion in half, running from root end, up to the shoot. Place the onion cut side down and chop off the shoot ends, leaving the root attached to hold the onion together. Peel away the skin from the onion halves. Turn the onion so the shoot end is facing you. Cut down right through the onion half at intervals 3 mm apart. Turn the onion half around a quarter and laterally cut twice from the shoot end towards the root, once at 1/3 height and then again at 2/3's height, but don't cut all the way through (mind your fingers at this stage). Cut down through the onion, again at 3 mm intervals, so the tiny cubes fall away.
Peel the carrot and cut into 5 cm lengths. Cut away one side, around 5 mm in so you have a sturdy base on which to sit the carrot pieces. Place the carrots, base side down and cut lengthways into 3 mm wide wedges. Form a pile of 3 of these wedges and cut them into 3 mm wide sticks. Turn the sticks around and cut them into tiny dice. The procedure for the celery is much the same as the carrots, no need to peel them of course.