Chop the onions, celery, and carrots in a 2:1:1 ratio
Heat olive oil (or butter) in a pan
Saute the chopped vegetables in the pan until they soften and become golden in color
Add other ingredients such as rice, meat, broth, tomatoes, etc.
Cook for about 5 minutes
Use the chopped soffritto as a flavor base for soups, sauces, stews, or braises