Prepare Ingredients:

• Grate the onion onto paper towels and squeeze out excess moisture.

• Grate frozen butter using the same grater.

Mix Burger Mixture:

• In a large bowl, combine ground chicken, grated onion, frozen butter, garlic, Worcestershire sauce, mayonnaise, Dijon mustard, lemon zest, liquid smoke (if using), and parmesan cheese. Mix until just combined.

Form Patties:

• Divide the mixture into 4 equal portions and form into patties about ½–¾ inch thick.

• Press a thumbprint indentation into the center of each patty and season both sides with kosher salt and black pepper.

Chill:

• Place patties on a parchment-lined baking sheet and freeze for 20 minutes to firm up.

Grill:

• Preheat the grill to medium-high heat and oil the grates.

• Grill the burgers for 5–6 minutes per side, until the internal temperature reaches 160°F.

Rest & Assemble:

• Let burgers rest for 5 minutes.

• Assemble each burger on a toasted bun with romaine lettuce, Caesar dressing, red onion, shaved parmesan, and croutons.

• Serve immediately and enjoy!