1/2 cup butter
4 onions, thinly sliced
1 teaspoon sugar
1/2 teaspoon salt, divided
1 sprig thyme
1/2 teaspoon black pepper
1/2 cup white wine
1/2 cup beef broth
4 chicken breasts
1 cup shredded Gruyère cheese
Preheat the oven to 400 degrees F.
Melt the butter in a heavy-bottomed skillet, and add the onions, sugar, a pinch of salt and thyme. Cook, stirring occasionally, for about 25 minutes, or until the onions are very caramelized.
Add the pepper and white wine, and reduce until all of the liquid has evaporated.
Add the beef broth, bring to a boil, and remove from the heat.
Season the chicken breasts with the remaining salt. Remove the sprig of thyme from the onions, and pour them over the chicken.
Bake for 25 minutes, and remove from the oven and top with the shredded cheese. Return to the oven and continue baking for an additional 5 minutes, or until the cheese is bubbly.
Remove from the oven and allow to cool 5 to 10 minutes before serving.