4 Medium yellow onions, thinly sliced
1/4 cup Dry white wine
2 tablespoons Thyme leaves, fresh
1 cup Sharp white cheddar, grated
1 cup Gruyere cheese, grated
8 teaspoons Dijon mustard
8 slices Crusty bread, thick slices, such as sourdough
Place butter in a medium saucepan over medium heat. When melted, add the onions and cook until the onions begin to soften, about 4 minutes. Season with salt. Reduce the heat to medium low and continue to cook until the onions soften and brown almost to the consistency of a jam. Deglaze the pan with a little bit of water throughout cooking to prevent the onions from burning.
Once the onions are almost to a jam-like consistency, add the thyme leaves and deglaze with the white wine. Cook for another minute or two. Remove from the heat and allow to cool slightly.
Butter one side of each piece of bread and place them buttered-side-down on the cutting board. Spread 1 teaspoon of mustard on each slice. Top four slices with ¼ cup cheese, quarter of the onions, and another ¼ cup cheese. Place a second slice of bread on top.
Heat a heavy nonstick sauté pan over medium or medium-low heat. Add the sandwich and allow to cook until golden brown and melted, 2 to 3 minutes per side. If one side is burning, be sure to turn the heat down further! Continue cooking the remaining sandwiches. Slice and serve.
Upgrade a regular grilled cheese with this ooey, gooey French onion grilled cheese recipe.
Prep time: 15 minutes
Cook time: 45 minutes