I always slice the stems very thin and dehydrate. Then using a spice or coffee grinder I grind them into a powder. Used in soups stews or sauces you get vegetables with no vegetable flavor. Only thing you have to watch out for is color. I once added a couple tablespoons to turkey rice soup and it turned the broth pea green. Didn't affect the taste but looked a little odd. This is also a good use for any excess vegetables from yhe garden.
Dennis