Smash Burger Recipe - Petite Panini

Ingredients

• 450 g ground beef
• 1 tsp salt
• 0.5 tsp black pepper
• 4 burger buns
• 4 slices cheddar cheese
• 1 tbsp unsalted butter
• 4 leaves iceberg lettuce
• 4 slices tomato
• 4 slices dill pickles
• 4 tbsp mayonnaise
• 2 tbsp ketchup
• 1 tbsp yellow mustard
• 0.5 small red onion