What the F* is a Soffritto?

http://proximalkitchen.blogspot.com/2010/08/carbo-loading-tagliatelle-alla.html

This is an essential piece of knowledge for any self respecting foodie/cook - Clementine and I had an argument heated discussion about it this morning over breakfast, including RE its spelling.
I was perplexed as to why it wasn't a part of the lasagne recipe I recently used (can be found HERE)

AKA: mirepoix (french), refogado (portugese), sofrito (spanish)

A soffritto is the flavour base of many sauces, soups and stews e.g. bolognese sauces, minestrone; it normally consists of celery, carrot and onion. The vegetables are diced (all the same size) and sautéed with olive oil and/or butter.
The italian version can also include garlic and in some recipes the onion is swapped out for leeks or shallots.