The yardstick most often trotted out to assess cooking abilities is 'how to boil an egg'. Actually, boiling an egg is not that straightforward, and the news media usually manage to come up with the wrong answer anyway. A much better test would be soffrito.
Soffrito comes from the Italian 'to fry gently' but the technique has wide applications in cookery and forms the basis of many well known dishes - yes, even spag bol. Indeed, its origins can be traced back to a mediaeval Catalan manuscript, the Libre de Sent Sovi and the method has its counterpart in the Catalan sofregit and Castillian sofrito. Whatever the origin, some aromatic vegetables are gently fried in oil until soft. Sounds easy enough, but some common sense and attention to detail makes all the difference. Here are a few tips:
Any pan will do but a heavy bottomed skillet, saute or frying pan is best. The idea is to cook it slowly and a heavy pan will diffuse the heat better. Don't use a lid -- you don't want it to steam.
Depending on what the soffrito is a base for, you can use butter, oil or a mixture of the two. A good quality olive oil is best in most instances. Use enough to coat the ingredients properly but not so much that they swim in it!
The traditional Italian soffrito is a mixture of onion, carrot and celery, finely chopped. The proportions are a matter of taste and availability, but one medium onion, one medium carrot and a stick of celery is typical and sufficient for a dish for four people. You can include green, red or yellow pepper (capiscum), pancetta (bacon), chorizo or anything else that strikes your fancy, in any permutation. Garlic is usually a must, but is best added towards the end of cooking to avoid scorching.
Soffrito can be seasoned with black pepper, fresh parsley, bay leaf, rosemary or other herbs to taste, depending on the final dish. However it is best to avoid salt -- it can be added later -- as this tends to draw out moisture so that the ingredients stew rather than fry.
Start with a fairly hot pan but turn down the heat as low as possible as soon as the ingredients begin to sizzle. Cook very slowly, stirring occasionally: don't let it burn! Depending on the quantity, it may take 20-40 mins. The result should be perfectly soft without a hint of bite, and lightly golden.