Pastrami and Caramelized Onion Grilled Cheese.

Bahan-bahan (2 porsi)

• 1 1/2 tablespoons unsalted butter (plus more if needed)
• 1 small onion (thinly sliced)
• 1/2 tablespoon sugar
• Kosher salt and freshly ground pepper
• 3/4 cup dark beer
• 2 ounces deli-shaved pastrami or deli-sliced corned beef or leftover corned beef (cut into strips)
• 2 teaspoons Worcestershire sauce
• 1 tablespoon whole-grain mustard
• 1 1/2 cups grated Jarlsberg cheese (about 6 ounces)
• 4 slices pumpernickel or dark rye bread