Savory Mushroom and Barley Casserole with Caramelized Onions

Quick Recipe Version (TL;DR)

• Yield: 6 servings
• Prep Time: 25 minutes
• Cook Time: 1 hour 20 minutes
• Total Time: 1 hour 45 minutes

Quick Ingredients

• 2 tbsp olive oil
• 2 tbsp unsalted butter
• 2 large yellow onions, thinly sliced
• 3 cloves garlic, minced
• 12 oz cremini mushrooms, sliced
• 4 oz shiitake mushrooms, sliced
• 1 1/2 cups pearl barley, rinsed and drained
• 3 1/2 cups low-sodium vegetable or beef broth
• 1/2 cup dry white wine (or extra broth)
• 2 tsp fresh thyme leaves (or 1 tsp dried)
• 1 tsp finely chopped fresh rosemary (or 1/2 tsp dried)
• 1 bay leaf
• 1 to 1 1/4 tsp kosher salt, to taste
• 1/2 tsp freshly ground black pepper
• Optional: 1/2 cup grated Parmesan, 2 tbsp chopped fresh parsley

Do This

• 1. Preheat oven to 375°F (190°C). Grease a 2 to 3-quart baking dish.
• 2. Slowly caramelize onions in olive oil and butter over medium-low heat, 20–25 minutes.
• 3. Add garlic; cook 1 minute. Stir in mushrooms; sauté until they release liquid and brown, 8–10 minutes.
• 4. Add barley and herbs; toast 2–3 minutes. Deglaze with wine, scraping browned bits.
• 5. Stir in broth, salt, and pepper; bring to a simmer, then transfer everything to the baking dish.
• 6. Cover tightly and bake 40 minutes. Uncover and bake 15–20 minutes more, until barley is tender and liquid absorbed.
• 7. Rest 10 minutes. Fluff, adjust seasoning, and top with Parmesan and parsley if using.

---

Why You’ll Love This Recipe

• Deep, earthy flavor from mushrooms, herbs, and slow-caramelized onions.
• Hearty and comforting, perfect for chilly nights as a side or vegetarian main.
• Baked in one dish after a quick stovetop start, making it cozy and mostly hands-off.
• Flexible and forgiving: easy to adapt with different broths, cheeses, or add-ins.

Grocery List

• Produce: Yellow onions, garlic, cremini mushrooms, shiitake mushrooms, fresh thyme, fresh rosemary, fresh parsley (optional).
• Dairy: Unsalted butter, grated Parmesan cheese (optional).
• Pantry: Pearl barley, olive oil, low-sodium vegetable or beef broth, dry white wine (or extra broth), bay leaf, kosher salt, black pepper, nonstick spray or extra oil for greasing.

Full Ingredients

Casserole Base

• 2 tbsp olive oil
• 2 tbsp unsalted butter
• 2 large yellow onions, thinly sliced (about 1 1/2 lb / 680 g total)
• 3 cloves garlic, minced
• 12 oz (340 g) cremini or baby bella mushrooms, cleaned and sliced
• 4 oz (115 g) shiitake mushrooms, stems removed and caps sliced
• 1 1/2 cups (285 g) pearl barley, rinsed and drained
• 1/2 cup (120 ml) dry white wine (or additional broth)
• 3 1/2 cups (830 ml) low-sodium vegetable or beef broth
• 2 tsp fresh thyme leaves, chopped (or 1 tsp dried thyme)
• 1 tsp finely chopped fresh rosemary (or 1/2 tsp dried rosemary)
• 1 bay leaf
• 1 to 1 1/4 tsp kosher salt, plus more to taste
• 1/2 tsp freshly ground black pepper, plus more to taste

For the Pan and Finishing

• Oil or nonstick spray, for greasing the baking dish
• 1/2 cup (45 g) freshly grated Parmesan cheese (optional, for topping)
• 2 tbsp chopped fresh flat-leaf parsley (optional, for garnish)

Step-by-Step Instructions

Step 1: Preheat the oven and prepare the baking dish

Preheat your oven to 375°F (190°C) with a rack in the center. Lightly grease a 2 to 3-quart (about 2–3 liter) baking dish or casserole with a little olive oil or nonstick spray. A deep ceramic dish or a wide cast iron skillet works especially well for even baking and a rustic presentation.

Step 2: Slowly caramelize the onions

In a large, heavy skillet or Dutch oven, heat the olive oil and butter over medium heat until the butter is melted and foamy. Add the sliced onions and a small pinch of salt. Stir to coat them in the fat, then reduce the heat to medium-low.

Cook the onions, stirring every few minutes, until they soften, turn golden, and become jammy and deeply fragrant, about 20–25 minutes. If they start to brown too quickly, lower the heat and add a splash of water to loosen any browned bits. You are aiming for a deep golden color, not dark brown or burnt.

Step 3: Add garlic and cook the mushrooms

When the onions are caramelized, stir in the minced garlic and cook for about 30–60 seconds until fragrant.

Add the sliced cremini and shiitake mushrooms to the pan. Increase the heat to medium and cook, stirring occasionally, until the mushrooms release their liquid, that liquid evaporates, and the mushrooms start to brown, about 8–10 minutes. Season with a pinch of salt and pepper to start layering flavor.

Step 4: Toast the barley and deglaze with wine

Add the rinsed and drained pearl barley to the pan with the onions and mushrooms. Sprinkle in the thyme, rosemary, and the bay leaf. Stir well and cook for 2–3 minutes to lightly toast the barley and bloom the herbs. You should start to smell a nutty, toasty aroma.

Pour in the white wine (or additional broth), scraping up any browned bits from the bottom of the pan with a wooden spoon. Let the wine simmer for 2–3 minutes, until it is mostly absorbed and the pan looks almost dry again.

Step 5: Add broth and transfer to the baking dish

Pour in the broth and add 1 tsp of kosher salt and the 1/2 tsp black pepper. Stir everything together and bring the mixture just up to a gentle simmer. Taste the liquid carefully and add up to an additional 1/4 tsp salt if needed; it should be pleasantly seasoned, as the barley will absorb much of this flavor.

Carefully transfer the entire mixture to your prepared baking dish, spreading the barley out evenly. Make sure all the grains are submerged in liquid. Cover the dish tightly with a lid or a double layer of foil to keep in the steam.

Step 6: Bake until the barley is tender

Place the covered dish in the preheated oven and bake for 40 minutes. Then carefully remove the lid or foil and check the barley. It will still be a bit firm and there should still be some liquid in the dish.

Return the casserole to the oven, uncovered, and bake for an additional 15–20 minutes, or until the barley is tender but pleasantly chewy and most of the liquid has been absorbed. The top should look slightly browned and the edges may be bubbling.

Step 7: Rest, finish, and serve

Remove the casserole from the oven and discard the bay leaf. Let it rest for 10 minutes; this allows the barley to finish absorbing any remaining liquid and makes it easier to serve clean portions.

Fluff the casserole gently with a fork, mixing the mushrooms and onions throughout. Taste and adjust seasoning with additional salt and pepper if needed. If using, sprinkle the top with grated Parmesan and chopped parsley just before serving. Serve warm as a cozy main dish or as a hearty side alongside roasted meats or a crisp green salad.

Pro Tips

• Rinse the barley well: Rinsing removes excess starch and any dust, helping the grains cook up fluffy rather than gummy.
• Do not rush the onions: True caramelized onions take time. Keeping the heat low and stirring occasionally builds deep sweetness and flavor.
• Use mixed mushrooms: Combining cremini and shiitake (or even adding oyster or portobello) adds complexity and a meatier texture.
• Taste the broth before baking: The barley will soak up whatever is in the pan, so adjust salt and herbs at this stage for the best flavor.
• Let it rest: The 10-minute rest after baking helps the casserole set and prevents it from being soupy when scooped.

Variations

• Cheesy gratin style: After baking uncovered, sprinkle the top with an extra 1/2 cup of grated Gruyère or Fontina and broil for 2–3 minutes until bubbly and browned.
• Add greens: Stir in 3–4 cups of roughly chopped kale or spinach during the last 10 minutes of baking for extra color and nutrition.
• Meaty version: Brown 6 oz (170 g) of diced pancetta or smoked sausage at the beginning, remove, then cook the onions in the rendered fat. Stir the meat back in before baking.

Storage & Make-Ahead

Let the casserole cool to room temperature, then cover tightly and refrigerate for up to 3–4 days. Reheat individual portions in the microwave with a splash of broth or water, or rewarm the whole dish, covered, in a 325°F (165°C) oven for 20–25 minutes until hot throughout.

For longer storage, portion the cooled casserole into airtight containers and freeze for up to 2–3 months. Thaw overnight in the refrigerator before reheating. To make ahead, you can assemble the casserole up to the point of baking, cover, and refrigerate for up to 24 hours. Add an extra 5–10 minutes to the covered baking time if starting from cold.

Nutrition (per serving)

Approximate values for 1 of 6 servings (without optional cheese): about 290 calories, 8 g protein, 48 g carbohydrates, 7 g fiber, 7 g fat, 2.5 g saturated fat, 0 mg cholesterol, and around 600 mg sodium (will vary based on broth and added salt). Adding Parmesan will increase protein, fat, and sodium slightly.