Salt and pepper the stew meat.
Turn on the “Saute” function for the Instant Pot. Heat olive oil in the bowl and then, working in batches, brown the stew meat. (The meat should not be cooked completely, just browned). As each batch browns, transfer to a clean plate and set aside.
Once all of the stew meat is browned, saute onion in the Instant Pot bowl, then pour in 1 cup of water. Scrape along the bottom of the bowl to release the “browned bits” of stew meat and onion that may be stuck on the bottom. (Your Instant Pot may read “Hot” or “Burn” at this point. Don’t panic—this last step will not only add amazing flavor to the soup, but it should cancel the “Hot” notice since you are releasing the scraps of food that are causing the message).
Once the bottom is scraped clean, stir in remaining water, beef base, celery, carrots, and garlic. Return the stew meat to the pot and stir to combine.
Seal Instant Pot and set valve to “Sealing”. Select the “Manual” option on the pot settings and adjust time to 30 minutes.
Once cooking time is complete, let the Instant Pot sit for 12–15 minutes. After that time, quick release pressure, carefully turning the valve to the venting position.
Remove the Instant Pot lid and change the setting to “Soup/Broth” or “Saute”. This setting should bring the soup to a rolling boil. Once the soup begins to boil, stir in the shredded potato (I use a small Russet potato, peeled and shredded). Let potato cook for about 5–10 minutes. As the potato cooks, it slightly dissolves and thickens the soup.
Once the shredded potato has cooked slightly, add the quick barley. Stir to combine and cook an additional 10–15 minutes, or according to the package instructions.
Check the broth and if needed, add the Worcestershire sauce and more salt and pepper to taste.
To make in a slow cooker, brown the meat in a large stock pot. Remove to a clean plate. Pour in 1 cup of water and scrape the bottom of the pan to release the stuck on “brown bits”. Add remaining water. Into the slow cooker, put browned meat, water, beef base, celery, onion, carrots, and garlic. Cook on low 7 hours. After 7 hours, add shredded potato. Stir to combine, cover and cook an additional hour. Then stir in barley, cover and cook for an additional 15–30 minutes or until barley is tender.