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Cheesy French Onion Chicken Sandwich

Cheesy French Onion Chicken Sandwich

This might be the best thing I’ve EVER made. If French onion soup and a grilled chicken sandwich had a baby, this would be it.
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Prep Time 20 minutes
Cook Time 45 minutes
Total Time 1 hour 5 minutes
Servings: 4 servings
Course: Lunch
Ingredients Method Notes

Ingredients
  

  • 3 large yellow onions thinly sliced
  • 1 tbsp butter
  • 1 tbsp olive oil
  • 1 tsp salt
  • 1 tsp sugar
  • 2 sprigs fresh thyme
  • 1/4 cup beef broth
  • 1 tbsp balsamic vinegar
  • 2 boneless skinless chicken breasts
  • 1 tsp garlic powder
  • 1 tsp onion powder
  • 1 tsp smoked paprika
  • 1 tsp salt
  • 1 tsp pepper
  • 1 tbsp olive oil
  • 1/2 cup mayo
  • 2 cloves garlic minced
  • 1 tsp dijon mustard
  • 1 tsp lemon juice
  • 1 finely chopped fresh thyme
  • 1 to taste salt & pepper
  • 1 cup beef broth
  • 1 tsp Worcestershire
  • 2 cloves garlic minced
  • 2 sprigs thyme
  • 1 pinch salt & pepper
  • 4 thick slices sourdough or ciabatta
  • 8 oz gruyère cheese shredded
  • 2 slices Swiss cheese

Method
 

  1. Whisk together the aioli ingredients and chill while cooking.
  1. Melt butter with olive oil over medium-low heat. Add onions, salt, sugar, and thyme. Cook for 30–35 minutes, stirring occasionally, until deeply golden and jammy.
  1. Add beef broth and balsamic vinegar to deglaze the pan, scraping up the flavorful brown bits. Cook until mostly reduced and set aside.
  1. Season the chicken on both sides with garlic powder, onion powder, smoked paprika, salt, and pepper.
  1. Heat butter and olive oil over medium-high heat. Sear the chicken for 3–4 minutes per side until cooked through. Top with Swiss cheese in the last minute and cover to melt. Let the chicken rest.
  1. In the same pan, add beef broth, Worcestershire, garlic, and thyme. Simmer for 5 minutes, scraping up the fond. Pour into a bowl for dipping.
  1. Brush the bread lightly with oil or butter, top with gruyère cheese, and toast at 350°F for 3–5 minutes.
  1. Spread aioli on the toasted bread, add the chicken, pile on the caramelized onions, and serve with hot au jus for dipping.

Notes

  • Make sure to slice the onions evenly to ensure they caramelize uniformly.
  • Let the chicken rest after cooking to retain its juices.
  • Toast the bread just before assembling to keep it crispy.
  • For extra flavor, you can add a splash of white wine while deglazing the onions.
  • If you prefer a spicier kick, add a pinch of cayenne pepper to the aioli.