Soak the sliced onions in ice water for a minimum of 2 hours.
Preheat the vegetable oil to 375 degrees F. After soaking the rings, drain well and toss in the flour. Fry until golden brown, then season with salt and pepper.
To prepare the burger, in a bowl, blend the ground beef with 1 teaspoon salt and 1/2 teaspoon pepper. Then remove a small portion, about 1 ounce, and cook to check level of seasoning.
Re-season the beef if necessary. To form patties, portion four 7 1/2- to 8-ounce rounds. Flatten the top with a 5-inch disk, ensuring not to over-mix during the process.
Once portioned, warm a griddle or pan over medium high heat until hot, 2 to 3 minutes. Then add the grapeseed oil and patties. Reduce the heat to medium. Cook on first side until browned, 3 minutes, then flip and repeat process to desired temperature. Remove from the heat and rest.
While the meat is resting, cook the fries until golden brown in the same oil used for the onion rings. When finished, remove and season with salt and pepper. Then warm a medium flat pan over medium heat. Spread the butter on all of the buns. Brown the buns in the pan until solid brown texture is achieved, 1 to 2 minutes. Then remove from the heat and set aside until ready to serve.
In a bowl, blend the shredded lettuce with the Thousand Island dressing, tossing well. Then top the browned buns with the lettuce, a cooked patty and some onion rings and top with the bun top. Serve with the French fries.