For cooking separately, I cook 1 c barley to 2½ c water, plus a tsp of salt. Then, I pressure cook it in the IP for 20 min, and let the pressure release naturally. This will leave a little more liquid than 2 c, which will be fairly dry, and since I'm usually rinsing this separately cooked barley, like for the salad recently, I'd rather have it liquidy, than with the liquid totally absorbed, like with rice, as it is hard to separate - sort of like sticky rice, except really sticky!
As for cooking it separately, I don't do this with soups, as barley is sort of hard to overcook, like pasta! For mushroom barley soup, however, I do cook the mushrooms separately, and cook them briefly at the end, with the rest of the soup. This way, most of the flavor is still in them. But I almost always add some dried boletus mushrooms, and sometimes some duxelles, if I have some on hand in the freezer. These will add a lot of flavor, when cooked with the initial ingredients. And I like barley so much that I usually use 3/4 c, to 6-7 c water or broth, and a pound of mushrooms, while most similarly sized recipes usually call for 3-4 tb. Why bother?
My typical recipe would start soaking 3/4 oz boletus or porcini in hot water, then chop up a good sized onion, 4 cloves garlic, and a generous tb of fresh rosemary. Then I cut up the mushrooms, quartered, if small, sliced thick, if large, and set aside. Then I wash the sand out of the boletus, strain the soaking water, and do this at least twice, saving the water, then I mince up the boletus very fine. Then measure out, and rinse the 3/4 c pearl barley, and drain.
I start with about 4 tb olive oil on Sauté medium, in the Instant Pot, or butter, if I add duxelles later, and cook until starting to brown. Then add garlic and rosemary, cook a minute, then add the boletus and strained liquid, turn off, then to Sauté high, and boil down almost completely, then add the water or broth, and bring to a boil, then hit o Off. I usually use thin soy sauce, for the salt, and grind some black pepper in. Then add the barley, a quarter cup or so of duxelles, if using, then set to Manual 25 min, put lid on, and seal, and let pressure release naturally, when finished. While cooking, I put the mushrooms in a NS wok (or about a 10" sauté pan), with about 2 tb water, cover, bring to a boil, and cook until cooked down, then uncover, and boil off water (this method makes it unnecessary to use a lot of oil, as with the fresh mushrooms). Then add just 2 tsp olive oil, and sauté about 6-7 min on med-high, tossing frequently, until browned well, then deglaze by adding just a little water, then set aside until barley mix is finished, then add, and simmer a few minutes. Correct seasoning, stir in 3-4 tb freshly chopped parsley, and enjoy.
One favorite recipe I remember had not as much barley, but some diced potato, as some extra starch, and leeks, as the allium in it. I don't recall the herb in that one (maybe some thyme, then some chopped parsley, at the end), but I only made it when I had help eating it, as the potatoes do overcook a little, like pasta, when reheated.
