Cremini mushrooms look a lot like white button mushroom
s, except they are browner on the outside. They have a much deeper flavor, and will produce a pretty dark, brothy liquor when cooked slowly with a little salt. They make excellent vegetarian gravy
Cremini mushrooms are sometimes labeled "baby bellas" in the supermarket. This is because a cremini mushroom that's allowed to grow really large (bigger than three inches across) magically becomes a portobello mushroom. Okay, it's not magic, but "portobellos" were invented in the 1980s as a slick way to sell overgrown, otherwise unsellable creminis. They do taste pretty good, though.