Set a large deep skillet with a lid over medium heat.

Add the olive oil and butter to the skillet and let the butter melt.

Add the sliced onions and 1 teaspoon salt to the skillet. Stir until the onions are coated in the fat.

Cook the onions for 8 minutes, stirring every few minutes, until they are soft and starting to shrink.

Lower the heat to medium-low and keep cooking the onions for 10 to 12 minutes more, stirring often, until they are deep golden brown. If they start to catch too fast, lower the heat a little.

Add the sliced mushrooms to the skillet with the onions.

Cook the mushrooms for 6 to 8 minutes, stirring now and then, until they give off their liquid and that liquid cooks away. The mushrooms should look browned at the edges, not wet.

Add the chopped garlic and chopped thyme to the skillet.

Cook for 1 minute, stirring, until the garlic smells fragrant and no longer looks raw.

Add the rinsed pearl barley to the skillet.

Stir the barley for 1 minute so it gets coated with the onion mixture and starts to smell a little toasty.

Pour the vegetable broth and soy sauce into the skillet. Add the black pepper and stir well, scraping the bottom of the skillet so nothing sticks there.