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Caramelized Onion and Mushroom Beef Casserole, fall casserole recipes comfort
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
Cook Time 50 minutes
Total Time 1 hour 15 minutes
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
  • 9x13-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 9x13-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.