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Cheesy French Onion Smashburger Casserole Bake

French Onion Smashburger Casserole - featured image
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A cozy, one-pan casserole that combines the bold flavors of a classic smashburger with the rich, caramelized goodness of French onion soup, all topped with a gooey, golden cheese layer. Perfect for busy weeknights or potlucks, this dish is hearty, satisfying, and a guaranteed crowd-pleaser.

Ingredients

Scale
  • 1 lb ground beef (80/20 blend)
  • 2 large yellow onions, thinly sliced
  • 2 cloves garlic, minced
  • 1 cup beef broth
  • 1 tbsp Worcestershire sauce
  • 1 tsp kosher salt (plus more to taste)
  • 1/2 tsp black pepper, freshly ground
  • 2 tsp dried thyme (or 1 tbsp fresh thyme)
  • 1 tsp sugar
  • 2 cups shredded Gruyère cheese (or Swiss or mozzarella)
  • 1 cup shredded sharp cheddar cheese
  • 1/2 cup sour cream
  • 2 tbsp unsalted butter, melted
  • 1/2 cup crispy fried onions (optional)
  • 1/4 cup chopped chives or parsley (optional)
  • 1 cup diced pickles (optional)

Instructions

  1. Preheat your oven to 375°F (190°C). Grease your casserole dish or skillet lightly with butter or oil.
  2. In your skillet over medium heat, melt 2 tablespoons of unsalted butter. Add the sliced onions and sprinkle with 1 teaspoon sugar and a pinch of salt. Cook, stirring every few minutes, for 15-20 minutes until the onions are golden brown and soft. Add a splash of beef broth if they start to stick.
  3. Stir in the minced garlic and cook for 1 minute. Pour in 1 cup beef broth and 1 tablespoon Worcestershire sauce. Scrape up any browned bits from the bottom and let simmer for 3-4 minutes until slightly reduced.
  4. Push the onions to the side and add the ground beef to the pan. Smash it down with your spatula. Season with 1 teaspoon salt, 1/2 teaspoon black pepper, and 2 teaspoons thyme. Cook, breaking up any large chunks, until beef is browned and just cooked through, about 5-7 minutes. Mix the onions and beef together.
  5. If using a separate baking dish, transfer the beef-onion mixture into it and spread evenly. If using a skillet, leave as is.
  6. In a bowl, combine 2 cups shredded Gruyère, 1 cup shredded cheddar, and 1/2 cup sour cream. Mix well. Spread this cheese blend over the beef-onion layer. Drizzle with 2 tablespoons melted butter.
  7. Bake uncovered for 20-25 minutes, until the cheese is bubbling and golden. If the cheese browns too quickly, cover loosely with foil for the last 10 minutes.
  8. Remove from oven and let cool for 5 minutes. Top with crispy fried onions, fresh herbs, or diced pickles if desired.
  9. Cut into squares and serve warm.

Notes

For best flavor, caramelize onions low and slow. Grate cheese fresh for a smoother melt. Let casserole rest 5 minutes before serving for clean slices. Make ahead by prepping onions and beef up to 2 days in advance. Store leftovers in the fridge for up to 4 days or freeze for up to 2 months. For gluten-free, check labels on Worcestershire sauce and crispy onions or omit them.

Nutrition

Keywords: smashburger casserole, French onion casserole, cheesy casserole, one-pan dinner, comfort food, ground beef casserole, easy weeknight dinner, skillet casserole, family dinner, potluck recipe

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