Turkey Burgers with Caramelized Onions

Instructions:

1. Heat butter and 15ml olive oil in a 12-inch cast iron skillet over medium-low heat. Add sliced onions and 3g salt, stirring occasionally for 15–20 minutes until deep mahogany brown.
2. Stir in the balsamic vinegar to deglaze the pan, scraping up the brown bits. Remove onions from the skillet and set aside.
3. In a medium mixing bowl, combine ground turkey, Worcestershire sauce, tomato paste, garlic powder, smoked paprika, 3g salt, and 1g black pepper. Mix gently by hand to avoid overworking the meat.
4. Form the mixture into four equal patties, pressing a slight indentation into the center of each to prevent doming during cooking.
5. Wipe the skillet clean and heat 15g olive oil over medium-high heat. Sear patties for 5–6 minutes per side until a deep brown crust forms and the internal temperature reaches the safe threshold.
6. During the final minute of cooking, place a slice of Swiss cheese on each patty to melt.
7. Toast the buns, spread with mayonnaise, and assemble burgers by layering the patty, caramelized onions, and baby arugula.