To assemble: Toast bun on a hot skillet with butter, until the edges are golden brown. Starting with the bottom bun, spread 1 tablespoon of spread on the bottom, and top with pickles, tomatoes, and lettuce. Add 1 burger patty, a heaping tablespoon of caramelized onions, and the second patty. Top that with french fries, more spread, and another scoop of onions. Finish with the top of the bun. Serve immediately.