Stems from portabella can be used for what

https://www.youtube.com/watch?v=wMXMz3gzolw this is a great interview check it out from 2:50 on it talks about Unami flavors and making a mushroom stock. watch the whole thing if you have time.

I find them to be too woody to use in most dishes. Maybe it's a regional thing. I have added them to other mushrooms and made duxelles. I loved the deep flavor they added. Other than that, I add them to my freezer bag of stock veggie scraps.

Chop finely, add a little pinch of fresh herbs and sautée. Add to a lovely omelette. The stems are tasty too, just not as visually appealing.

Mince them, saute with a little butter and swirl in some heavy cream. Spoon over toast.

Or with a fried egg: Mushrooms on Toast. https://food52.com/recipes/11176-mushrooms-on-toast

Agree with all of the above. If you only have a few leftover, they can be minced and add a great savoury/unami flavour to anything from stew to stir-fry.

I keep a ziplock bag in my freezer and toss in vegetable trimming, chicken bones, corn cobs, etc in there, and when one (or two) fill up I make stock. The stems would go in that bag in my house and add a great depth of flavor to the stock ...

Can I assume you bought portabella mushrooms and used the cap for say a mushroom burger? In many recipes the entire protabella is used, cap and stem. Unlike shitake mushrooms where the stems are woody, the stems of portabella mushrooms can be tender and tasty. Unless you have a recipe where the visual look of the mushroom is necessary, I use the stem portion. You can chop them, saute with onions or shallots, season with thyme and balsamic vinegar or a bit of cream and use them as a "caviar" style spread. There are many recipes on the web for these types of mushroom spreads. So unless the stems are woody, I see no reason not to cook with them.

broth