Divide the ground beef into 4 equal parts and form into balls. Place in the refrigerator for about 30 minutes to chill.
Meanwhile, in a small bowl, whisk together the onion, jalapeno, mayonnaise and mustard.
Spread the butter on the top and bottoms of the buns and toast until lightly browned.
Heat and grease a large cast iron skillet or a flat griddle over medium-high heat. Place the meat on the skillet or grill. Place a piece of waxed paper on top and mash with a grill press or cast iron skillet until the meat is flattened. Remove the waxed paper.
Season each patty with the Original seasoning, or substitute.
Cook for about 2 minutes, or until browned, then flip the patties over. Top with one slice of cheddar cheese and cook for an additional 1 minute or until browned. Remove from the heat.
Spread the mayonnaise mixture on the underside of the top and bottom buns. Top each bun with 2 patties. Top with lettuce and tomato. Serve immediately.