In-N-Out's Double-Double, Animal Style

INGREDIENTS

• 1/2 pound fresh beef chuck with plenty of fat, cut into 1-inch cubes
• 2 teaspoons vegetable oil, divided
• 1 large onion, finely chopped (about 1 1/2 cups)
• Kosher salt
• 2 tablespoons plus 2 teaspoons mayonnaise
• 1 tablespoon ketchup
• 2 teaspoons sweet pickle relish
• 1/2 teaspoon sugar
• 1/2 teaspoon distilled white vinegar
• 2 soft Hamburger buns, preferably
• Freshly ground black pepper
• 8 dill pickles chips
• 2 quarter-inch-thick slices ripe tomato
• 2 leaves fresh iceberg lettuce, white core section removed, torn to bun-sized pieces
• 1/4 cup yellow mustard
• 4 slices deli-cut American Cheese