4 cups minced onion
2-3 cups minced celery
2-3 cups minced carrot or fennel bulb (or a mixture of both)
2-3 cups olive oil
You can use a food processor to mince all the vegetables except the onion. (Onions will simply liquefy in a processor or blender. Chop the onions by hand using a very sharp knife.) For the other vegetables, process until pieces are quite small, but be sure to stop before they start to liquefy.
Heat a large pan (preferably a sauteuse with high sides) over medium heat. When warm, add the oil. When the oil starts to warm, add the vegetables and stir to coat all the vegetables with oil.
Cook gently, stirring every so often to prevent sticking, until the vegetables turn a golden straw color. This can take up to 45 minutes.
When they are golden blond, the soffritto is ready. You can refrigerate or freeze it until needed.
If you wish to make a darker soffritto, remove the amount you wish to keep lighter and continue cooking until the soffritto is an amber color, or as dark as you wish. Remember, if you have a small amount in a larger pan you must be vigilant to prevent burning, so turn down the heat and keep an eye out, or transfer to a smaller pan and keep the heat low.
Keeps a week in the refrigerator or about 6 months in the freezer.
For more information, see article How to Make Soffritto.