Make Burger Sauce: Add the classic Burger Sauce ingredients to a small bowl, stir to combine. Set aside.

Prep Onions + Butter: Place a cheese grater on top of 2-3 pieces of paper towel. Grate the white onion on top of the paper towel. Use the paper towel to gently squeeze out as much of the excess moisture from the onion. Set onions aside. Use the same cheese grater to shred the frozen butter (if using).

Prep Turkey Burger Balls: In a large bowl combine ground turkey, grated white onion, grated butter, garlic, worcestershire, mayo, dijon, lemon zest, liquid smoke and parmesan cheese. Use a scale to create 1/4 pound balls with your hands and set aside (will make approx. 5-6 balls).

Prep Other Ingredients: Butter both sides of the buns. Make the quick-pickled onions, if using. Have cheese ready to go, some salt + pepper for seasoning, as well as an extra plate to put your cooked burgers on. Having everything prepped and ready to go is essential, because the cook time goes real quick. 

Cook Burgers + Toast Buns: Place burger balls on preheated flat top. Slowly press down on each ball to flatten until the patties are approx. 1/4 inch thick. This will take 15-20 seconds per burger. Let sit and cook for the next 40 seconds (feel free to season patties at this point if you want). Flip and immediately add a slice of cheese to each - this is also when you will put the burger buns on the flat top griddle (buttered side down). Close lid and let burgers cook approx. 2 minutes. Open lid and remove burgers and buns to clean plate.

Build + Serve Burger: Take a toasted bun and place the cooked burger on top (or stack two turkey patties). Top with burger sauce, quick pickled onions and avocado. Enjoy!