The Quad D: Daddy Dutch Double Deluxe from Smashed: 60 Epic Smash Burgers and Sandwiches for Dinner,

Ingredients

• 1 tablespoon (14 g) butter
• 4 teaspoons (16 g) seasoned salt (We use Uncle Steve’s Lucky Shake All Purpose or Lawry’s Seasoned Salt.)
• 2 teaspoons pepper (to taste)
• 2 teaspoons salt (to taste)
• 1 pound (455 g) 80/20 ground beef, divided into four 4-ounce (115 g) loosely packed meatballs
• 1 tablespoon (15 ml) vegetable oil
• 2 cups (140 g) mushrooms, sliced
• 1 cup (115 g) sliced yellow onion
• Mayonnaise, for topping
• additional 1 tablespoon (14 g) mayonnaise, for toasting the buns
• 4 slices American cheese
• 2 hamburger buns