Caramelized Onion and Mushroom Beef Casserole

From the roundup: 24 Fall Casserole Recipes for Cozy Comfort Dinners

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One casserole dish of caramelized onion and mushroom beef casserole reliably feeds all seven of us with enough left over that two of the kids take it for lunch the next day, which almost never happens with a beef dinner in this house. The onions are the part that cannot be rushed. I learned that the hard way the first time I made this, when I gave them about eight minutes instead of twenty-five and the whole top layer tasted sharp instead of sweet. Pull them low and slow until they go deeply golden, then let the mushrooms and beef do the rest underneath that Gruyere and bread topping that gets just crispy enough around the edges.

Why you will love this

• The caramelized onions do the heavy lifting on flavor, so the seasoning stays simple.
• Mushrooms add enough bulk that you are not relying entirely on the beef to fill people up.
• The bread-and-Gruyere topping means you do not need to serve rolls or a starch on the side.
• You can assemble it the night before and pull it straight from the fridge to the oven.
• Leftovers reheat well at 350°F without getting watery or greasy.

Tips for success

• The onions need low, slow heat, at least 25 to 30 minutes. If they are browning fast in the first 10 minutes, your pan is too hot and they will turn bitter instead of sweet.
• If the pan looks dry while the onions cook, add a tablespoon of water and scrape up the bottom. That fond is flavor you do not want to lose.
• Day-old bread works better than fresh sandwich bread here. Fresh bread can get soggy under the cheese instead of holding its texture through the bake.
• Drain the beef well before layering. Extra grease in the pan will make the bottom of the casserole greasy rather than saucy.

If the top browns too fast

• Tent the casserole loosely with foil if the cheese is browning before the center is hot through.
• Remove the foil for the last 5 minutes if you want the bread to crisp back up.
• If you are reheating leftovers in the oven, add a splash of broth to the dish before covering with foil so the bread does not dry out completely.

Substitutions

Ground turkey works well in place of beef. Use beef broth either way for the depth the onions need, or swap in vegetable broth if you are going fully meatless with plant-based crumbles. Swiss, provolone, or even a sharp white cheddar can replace the Gruyere without changing the method at all.

For a gluten-light version, use your preferred gluten-free bread and swap the flour for a cornstarch slurry stirred into the liquid before it goes in the pan. The texture of the topping will be a little different but it still holds together.

Make-ahead and storage

Assemble the casserole, cover it tightly, and refrigerate up to 24 hours before baking. Pull it out while the oven preheats so it is not going in ice cold. Leftovers keep covered in the fridge for up to 4 days. Reheat individual portions in the microwave, or put the whole dish back in a 350°F oven covered with foil until heated through.

This casserole can be frozen, tightly wrapped, for up to 2 months. Thaw it overnight in the fridge before reheating. The bread topping will soften after freezing, so expect a less crisp texture on the top layer when reheated.

Front Porch Recipe

Caramelized Onion and Mushroom Beef Casserole

Slowly caramelized onions, savory mushrooms, and ground beef bake under a blanket of melted Gruyere and toasted bread for a deep, cozy casserole that tastes like French onion soup meets shepherd’s pie.

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Prep Time 25 minutes mins

Cook Time 50 minutes mins

Total Time 1 hour hr 15 minutes mins

Servings: 6 servings

Course: Dinner

Cuisine: French American

Calories: 520

Ingredients Equipment Method Notes

Ingredients

  

• 2 tbsp olive oil divided
• 2 tbsp unsalted butter
• 3 large yellow onions about 2 lbs, halved and thinly sliced
• 1 tsp kosher salt divided, plus more to taste
• 1 tsp sugar
• 1 lb cremini or baby bella mushrooms sliced
• 1 1/2 lbs ground beef 85% lean
• 3 cloves garlic minced
• 1 tbsp tomato paste
• 1 tbsp all-purpose flour
• 1 tsp fresh thyme leaves or 1/2 tsp dried
• 1/2 tsp black pepper
• 1 cup beef broth low-sodium
• 1 tbsp Worcestershire sauce
• 4 cups day-old crusty bread torn into 1-inch pieces
• 1 1/2 cups shredded Gruyere or Swiss cheese
• 2 tbsp fresh parsley chopped, for serving

Equipment

• large skillet
• 9×13-inch baking dish

Method

 

1. Heat 1 tablespoon oil and the butter in a large skillet over medium heat. Add onions, 1/2 teaspoon salt, and sugar. Cook 25 to 30 minutes, stirring often, until deep golden and caramelized. Lower heat if they brown too fast. Transfer onions to a bowl.
2. Add remaining oil to the skillet. Cook mushrooms with a pinch of salt for 6 to 8 minutes until browned and their liquid evaporates. Transfer to the onion bowl.
3. Add ground beef to the skillet. Cook 6 to 8 minutes until browned, breaking it up. Drain excess fat if needed. Stir in garlic, tomato paste, flour, thyme, remaining salt, and pepper for 1 minute.
4. Pour in beef broth and Worcestershire. Scrape up browned bits and simmer 3 to 4 minutes until slightly thickened. Stir the caramelized onions and mushrooms back in. Taste and adjust seasoning.
5. Heat the oven to 375°F. Spread the beef mixture in a greased 9×13-inch baking dish. Scatter bread pieces over the top and press lightly so some soak up the juices. Sprinkle Gruyere evenly over the bread.
6. Bake 20 to 25 minutes until the cheese is melted and the bread is toasted at the edges. Rest 5 minutes. Finish with parsley and serve.

Notes

Take your time caramelizing the onions, that sweetness is the backbone of the dish. Gruyere is ideal; Swiss or provolone also work.

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