French Onion Grilled Cheese

Ingredients

• unsalted butter
• large yellow onions, thinly sliced into half-moons
• kosher salt
• sprigs fresh thyme
• c. dry white wine
• slices crusty country-style bread
• unsalted butter, softened
• Freshly ground black pepper
• fresh thyme leaves
• Gruyère, thinly sliced