Onion Gratinée

Ingredients

• 2 tablespoons unsalted butter
• 6 shallots, peeled and sliced thin
• 2 lbs. yellow onions, peeled and sliced thin
• 1 tablespoon all-purpose flour
• 1/2 teaspoon fresh thyme leaves
• 1 cup white or red wine
• 1-quart low-sodium beef broth
• 1 tablespoon parsley, minced
• 8 (1/2-inch thick) slices baguette, toasted
• 1/2 lb Gruyère, shredded
• Kosher salt and black pepper, to taste