Combine ground beef, panko, Worcestershire, garlic powder, and salt & pepper in medium bowl. Form into patties (5-6 patties and then I do some singles and doubles on the buns or grab more buns) and chill.
In a separate small bowl combine sour cream and french onion soup mix. Mix well.
Heat your Blackstone or griddle on medium-high heat. When heated, place the patty’s on the Blackstone. Wait about a minute and then press down thoroughly with a press or weight. We like to put parchment paper on top of the burgers to allow for a mess-free process when pressing. Patty’s should be very thin, the thinner the better. Once cooked to your liking (we did about 3-4 min each side), flip the patty’s and press down again with spatula.
Optional: While burgers are cooking you can caramelize onions if using.
Place Gruyère cheese directly on the Blackstone in equal piles/circles. You want the same amount of piles of cheese to the patty quantity. Once the cheese starts to melt and patty’s are cooked, transfer each patty to each pile of cheese so it adheres to the patty. Let sit for 1 more minute. Place buns face down to toast.
Remove the Pattie’s and begin assembling your burger. Start by spreading your french onion spread on each half of the bun, layer on your patty(s), then add toppings: lettuce, tomato, caramelized onions and jalapeño.