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French Onion Chicken Casserole

So here's the deal - I had chicken thighs and a bag of onions, started caramelizing them low and slow, and the whole house started smelling like a French bistro. Threw some chicken in there, covered it with cheese, and it became one of those recipes you make all the time. The kind of dinner that makes you feel like you tried way harder than you actually did.
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Prep Time 15 minutes
Cook Time 1 hour
Total Time 1 hour 15 minutes
Servings: 6 servings
Course: Main Course
Cuisine: American, French
Calories: 485
Ingredients Equipment Method Notes

Ingredients
  

For the Chicken and Onions
  • 4 large yellow onions thinly sliced - seems like a lot but they cook down
  • 2 pounds boneless skinless chicken thighs don't use breasts, they'll dry out
  • 3 tablespoons butter this is where the magic happens
  • 2 tablespoons olive oil keeps the butter from burning
  • 4 cloves garlic minced, or use jarred when you're lazy
  • 1 cup beef broth makes it taste like French onion soup
  • 2 tablespoons fresh thyme leaves dried works but fresh is better here
  • 1 tablespoon balsamic vinegar secret ingredient
  • salt and pepper be generous
For the Topping
  • 2 cups shredded Gruyère cheese splurge on this if you can - it's worth it
  • 1 cup shredded mozzarella for that cheese pull
  • fresh parsley chopped, optional for prettiness

Equipment

  • Large skillet
  • 9x13 Baking Dish
  • Sharp Knife
  • Cutting Board
  • Wooden spoon

Method
 

  1. Get those onions going: Melt your butter with the olive oil in a big skillet over medium heat. Add all those sliced onions with a good pinch of salt. Cook for 25-30 minutes, stirring every few minutes. They'll reduce to like a quarter of their original volume and turn this gorgeous golden brown. Don't rush this part. Low and slow.
  2. Sear the chicken while you wait: Season your chicken thighs with salt, pepper, and about half the thyme. Once the onions are done and looking all caramelized, push them to one side of the pan. Sear the chicken in the empty space for 3-4 minutes per side til it's golden. It doesn't need to cook through yet - just get some color on it.
  3. Build your casserole: Grab a 9x13 baking dish (grease it a little) and lay the chicken pieces in there. Add the minced garlic to those caramelized onions in the pan, cook it for just a minute til it smells amazing, then pour in the beef broth, balsamic vinegar, and the rest of the thyme. Let it bubble for a couple minutes while you scrape up all those browned bits from the bottom. Pour this whole onion mixture over the chicken.
  4. Cheese it up and bake: Cover everything with your cheeses - mozzarella first, then Gruyère on top so it gets that golden crust. Stick it in a 375°F oven for 25-30 minutes. You want the chicken to hit 165°F inside and the cheese to be all bubbly and golden. Let it sit for 5 minutes before serving.

Notes

Sofia's tips: The onions take a while but you can walk away and do other stuff - just stir them every 5 minutes. Chicken thighs are cheaper than breasts and way juicier. When you add that broth, really scrape the pan - all those stuck bits are pure flavor.
Storage: Keeps in the fridge for 4-5 days. Great cold for lunch. Can freeze assembled but unbaked for up to 3 months.
Pro tip: Caramelize a huge batch of onions on Sunday and keep them in the fridge. Then this whole dish comes together in like 20 minutes during the week.