Rough chop onions so that slices are between ⅛ and ¼ inches thick.
Heat the butter and olive oil in a large saucepan on medium heat. Once the butter has melted, add onions and sweat them until they become translucent.
Reduce heat to low and continue to cook onions, stirring every 5-10 minutes to prevent them from sticking. Deglaze saucepan with a tablespoon or two of water or chicken stock when fond starts to form on the pan.
As onions continue to caramelize, continue stirring every 5-10 minutes and deglazing the saucepan as fond forms and the onions are no longer loose in the pan.
When the onions achieve a deep golden-brown (or dark brown) remove from heat and set aside.
Sauteed Mushrooms
In a cast-iron skillet, heat olive oil and butter over medium heat.
Add mushrooms and saute until they have released their water, approximately 2-3 minutes. Remove mushrooms from skillet and set aside.
Burger
Combine ground turkey with Worcestershire sauce, kosher salt, black pepper, breadcrumbs, garlic salt, onion powder, and chopped parsley.
Divide the turkey mixture into three equal portions and form them into patties. Place patties on a small baking sheet and refrigerate for 10-15 minutes.
In the same cast-iron skillet used to sautee the mushrooms, cook turkey patties for approximately 3-5 minutes on each side. When burgers have reached an internal temperature of 165 degrees top with cheese and cover until cheese has melted.
Serve burgers on a toasted bun and top with sauteed mushrooms and caramelized onions. Add additional toppings if desired.
Notes
1. Use a preheated cast-iron or nonstick skillet to get a browned seared exterior.2. Turkey burgers need to be cooked to an internal temperature of 165 degrees. Above 165 degrees and burgers will begin to dry out.3. To bind the patties together use breadcrumbs. It will also help the patties keep their shape.4. Turkey burgers are best served immediately when they are still juicy.5. Nutritional information is only an estimate. The accuracy of the nutritional information for any recipe on this site is not guaranteed. The nutritional value is only for the turkey burger patty, mushrooms, and caramelized onions. It does not include the nutritional values of the cheese and hamburger buns which will vary by brand and type. It does not include the nutrition for any substitutions.