Burger Bawang Oklahoma

Bahan-bahan (4 porsi)

• 1 1/2 pounds daging giling ((80/20 paling baik))
• 1 teaspoon garam halal
• 1/2 teaspoon cracked black pepper
• 1 white onion, (thinly sliced)
• 4 tablespoons butter, (divided)
• 4 slices keju Amerika
• 4 roti