Caramelize the onions

• Heat the oil in a pan over medium-low heat.
• Add the sliced onion and a pinch of salt.
• Cook slowly, stirring occasionally, until deeply golden brown and soft.

Make the dill burger sauce

• Mix the mayonnaise, ketchup, mustard, chopped dill pickle, paprika, garlic powder and black pepper until smooth.
• Set aside.

Toast the croissants

• Slice the croissants in half horizontally.
• Toast them cut side down in a pan over medium heat until lightly golden and slightly crisp.
• Remove and set aside.

Form the patties

• Divide the ground beef into two portions.
• Press each portion between pieces of parchment or paper to form thin patties.
• Season both sides with salt and black pepper.

Smash and cook the patties

• Heat a cast iron or stainless steel pan over high heat.
• Add the thin patties and cook without moving until the edges are crispy and browned.
• Flip, immediately add the cheese and cook until fully melted.

Assemble the burgers

• Spread dill burger sauce on the bottom half of each croissant.
• Add lettuce and tomato, then the cheesy patty and the caramelized onions.
• Add more sauce if desired and close with the top croissant.

Brush with parsley butter and serve

• Stir the chopped parsley and a pinch of salt into the melted butter.
• Brush generously over the tops of the croissants.
• Serve immediately while warm, crispy and glossy.