Preheat oven to 350 degrees.
Prepare vegetables by cutting as directed in the ingredients.
Heat a Dutch oven or oven-safe pot over medium-high heat; add butter, oil, mushrooms, and onion. Sauté until mushrooms have softened and onions are slightly translucent.
Add garlic and rosemary and sauté for another 30 seconds to allow flavors to bloom. Next, add barley and vegetable broth and stir to combine. Place lid on pot and place in oven. Bake for one hour.
After one hour, stir the barley to fluff. Taste and adjust seasonings to your liking. Garnish with fresh parsley, serve with your choice of protein and enjoy!