Make-Ahead Pizza Burgers

INGREDIENTS

• 1 onion, minced
• 3 stalks celery, minced
• 4 pounds ground beef
• 1 (32 ounce) bottle ketchup
• 1/2 (10.75 ounce) can condensed tomato soup
• 1/2 (6 ounce) can tomato paste
• 1 1/2 teaspoons garlic salt
• salt and ground black pepper to taste
• 1 1/2 (6 ounce) cans tomato paste
• 1 1/2 tablespoons dried oregano
• 1 1/2 tablespoons white sugar
• 1/4 cup butter, softened (optional)
• 36 English muffins, split
• 72 slices American cheese, cut into strips