The Portobellini mushroom is just another size variation of the well-know portobella (portabella) mushroom. The Portobellini is larger than a crimini but smaller than it's big brother the portobella. The mushroom has a light to medium-brown color and
At this stage (approximately 3" in diameter) both the mushroom and stem and can cooked or the stem can be removed so the mushroom can be easily stuffed or grilled then used whole in appetizers, for small burgers or even used in salads.
You can find these mushrooms at your local farmer's markets or even many well-stocked grocery stores. Canned mushrooms can even be found online at Amazon.com.