https://www.simplyrecipes.com/french-onion-chicken-recipe-8612553
Ingredients
5 tablespoons unsalted butter, divided
1 1/4 pounds boneless, skinless chicken breast tenderloins
1 1/2 teaspoons kosher salt, divided
3/4 teaspoon freshly ground black pepper, divided, plus more for garnish
1 large sweet onion, thinly sliced (about 3 cups)
1 tablespoon light brown sugar
2 tablespoons all-purpose flour
1 cup beef broth
2 tablespoons Worcestershire sauce
2 teaspoons chopped fresh thyme, plus more for garnish
4 ounces Swiss cheese, shredded (about 1 cup)