Smash burger, per SE - http://www.seriouseats.com/recipes/2014/03/ultra-smashed-cheeseburger-recipe-food-lab.html
5 ingredients - chuck steak, american cheese slice, hamburger bun, pickle, mayo. Not counting - salt & pepper to season meat & butter to toast bun.
Bonus - 3 Ingredient mac & cheese - http://www.seriouseats.com/recipes/2017/01/3-ingredient-stovetop-mac-and-cheese-recipe.html
Decent mac & cheese, but there are better. Pretty simple, though. Came out with too much sauce with these particular noodles.