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