Dice the onion and garlic, slice the carrots and celery, and quarter the mushrooms. If you are prepping this in advance to make at a later time, add these ingredients to a freezer bag with the dry barley. Add a label with the other ingredients you need and how long it will cook in the crockpot. Put it in the freezer and pull it out to thaw in the fridge a day before or the morning of the day you want to make the meal.
Add the veggies and barley to the slow cooker with the broth, bay leaf, dried thyme, and salt. Stir, cover, and cook for 3-4 hours on high or 6-8 hours on low.
Taste the soup before serving, and add salt or pepper to taste. Enjoy warm with crunchy bread!
This is intended to be a light and nutritious soup option, so you may find that you want to add or adjust the seasonings to your preference. If you are looking for more of a kick, add some lemon juice, fresh herbs, parmesan cheese, and/or hot sauce. Other seasoning ideas include garlic or onion powder, oregano, marjoram, and other dried Italian herbs.
Store in the fridge for 5-7 days. Reheat for ~2 minutes in the microwave, or in a saucepan on the stove over low-medium heat. You can also freeze this soup for up to 3 months in an airtight container. Thaw in the fridge overnight.
The barley will absorb more water the longer it is stored, so you may have to add a bit more liquid (water or broth) when reheating. If the soup gets congealed in the fridge, reheating it in a saucepan with a splash of liquid helps it return to its original consistency.
Depending on your crockpot, the soup may take longer than mine did to cook and thicken. Check the progress of the soup at 3 hours on high, or 6 hours on low, and cook for longer as needed.
Also, if you use hulled barley, the soup will likely take longer to cook than if you use pearled barley like the recipe suggests.