Also known as field mushrooms (and spelled ‘portabella’, ‘portobella’, and ‘portabello’), these are flat, dark open-capped mushrooms which can be 8cm to 10cm (3in to 4in) wide. They have a robust meaty texture making them good for roasting, baking and stuffing.
They're great for barbecuing, too - just dot with butter, crushed garlic, herbs and seasoning and cook for a few minutes until the juices run, or slice thickly and sauté with onions and garlic.