Kabob Koobideh (Persian Grilled Kebabs)

Ingredients (8)

• 1 medium yellow onion
• 1 pound 85% lean ground beef
• 1 teaspoon kosher salt
• 1/2 teaspoon freshly ground black pepper
• 1 tablespoon unsalted butter
• 1 tablespoon reserved onion juice
• 1 teaspoon freshly squeezed lemon juice
• 1/4 teaspoon fine sea salt