Mirepoix: two, one, one

Two parts onion, one carrot, one celery, by weight. The base under most of classical cooking — and the app's own name.

1. Cut to match the cooking time. A stock that runs six hours takes large chunks; a pan sauce that runs ten minutes takes a fine dice.
2. White mirepoix swaps the carrot for leek and parsnip. Use it whenever the finished dish must stay pale — carrot will tint a velouté the wrong colour.
3. For brown sauces the mirepoix is browned first, with the fat, before anything liquid goes near it. Browning it in the liquid gives you boiled vegetables, not colour.