Ingredients

• 1/2 pound Swiss cheese, grated
• 1/2 pound Gruyere cheese, grated
• 1 tablespoon cornstarch
• 3 tablespoons butter
• 2 large yellow onions, diced medium
• 10 ounces evaporated milk
• 2 teaspoons Worcestershire sauce
• 1 tablespoon finely chopped fresh thyme leaves
• Kosher salt and freshly ground black pepper

Directions

1. Place cheese in a medium bowl and toss with cornstarch until evenly coated. Set aside.
2. Melt butter in a medium saucepan over high heat. Add in onions and cook, stirring frequently, until bottom of saucepan is glazed in a pale brown fond, about 5 minutes. Add 2 tablespoons water and scrape up fond with wooden spoon. Continue to cook, stirring frequently, until fond has built up again, about 2 minutes longer. Add 2 more tablespoons water and scrape up browned bits. Repeat cooking, adding water, and scraping until onions are completely softened and a deep, dark brown, 20-30 minutes total. Transfer to a small bowl.
3. Place evaporated milk and Worcestershire sauce in now empty saucepan. Bring to a boil over medium-high heat, scraping bottom of pan with wooden spoon to release any remaining fond. Reduce heat to low and add in cheese. Stir constantly until cheese is melted and smooth. Stir in caramelized onions and thyme. Season with salt and pepper to taste. Transfer to a bowl and serve immediately.