Portobello mushrooms are simply cremini mushrooms that have been allowed to grow to their full size, about four to six inches in diameter.
When preparing button and cremini mushrooms, they are ready to be stuffed after they've been cleaned and have had the stems trimmed off.
For appetizers, button or cremini mushrooms work best while portobello mushrooms, with their wide caps, make a fabulous entrée.
Any mushroom will do, but I have found that button, Cremini, or even Portobello mushrooms add great flavor to this casserole.
Realistically, the best mushrooms for stuffing are button, cremini, or portobello mushrooms.
According to Gourmet Sleuth, portobello mushrooms are actually cremini type mushrooms.
This recipe fills 20 cremini mushrooms or four portobello mushrooms.