Onion Soup Gratine Recipe

Ingredients

• 2 tablespoons olive oil
• 2 1/2 pounds yellow onions, thinly sliced
• 2 large shallots, thinly sliced
• 3 leeks, thinly sliced
• 1 tablespoon kosher salt
• 3/4 teaspoon freshly ground black pepper
• 1 cup Marsala wine
• 2 teaspoons apple cider vinegar
• 8 cups vegetable or beef stock
• 2 garlic cloves, minced
• 2 large sprigs thyme
• 1 bay leaf
• 4 thick slices of artisan bread, toasted until crisp
• 2 tablespoons butter
• 1 medium clove garlic
• 1 pound Gruyere cheese, grated
• freshly minced chives, for garnish