How to Make It
Heat oven to 400° F. Heat the oil in a Dutch oven or large oven-safe saucepan over medium-high heat. Add the squash, onion, ¾ teaspoon salt, and ¼ teaspoon pepper and cook, stirring often, until the onion begins to soften, 4 to 6 minutes.
Add the barley to the vegetables and cook, stirring, for 1 minute. Add the wine and cook, stirring, until evaporated, about 1 minute. Add the broth and bring to a boil; cover the pot and transfer it to oven. Bake until the barley is tender, 35 to 40 minutes.
Stir in the spinach, Parmesan, and butter. Serve with additional Parmesan.