1 lb ground beef
4 slices of Swiss or gruyère cheese
2 large yellow onions, thinly sliced
2 tablespoons unsalted butter
1 tablespoon olive oil
1 teaspoon sugar
1 teaspoon balsamic vinegar
4 hamburger buns, toasted
1 teaspoon fresh thyme leaves
Salt and pepper to taste
1 clove garlic, minced
Optional: 1/4 cup beef broth
Directions
1. Begin by heating a large skillet over medium heat. Add butter and olive oil. Once the butter has melted, stir in your sliced onions, sugar, and balsamic vinegar. The sugar and vinegar help the onions attain that beautiful deep caramelization.
2.
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