Combine ground beef, salt and pepper in a medium bowl.
Divide into 4 equal-sized balls and then flatten each ball into thin patties.
Press down in the center of each patty with your thumb.
Bring a large cast-iron skillet to medium-high heat.
Add a 1/2 tablespoon of butter and let melt.
Add two patties to the pan and cook 3-4 minutes. Season the top of the patties with a little more kosher salt and pepper if you want (I usually do).
Flip and cook until the center reaches your desired doneness (135-145 degrees F. for medium rare); add cheese for the last 2 minutes of cook time.
Remove from skillet and let rest 5 minutes.
Add remaining 1/2 tablespoon of butter and repeat with remaining patties.
Build your burger: Add a little butter to the bottom and top bun. On the bottom bun add lettuce and one or two cheeseburgers followed by ketchup/mustard (or burger sauce), sliced onion and tomatoes. Place the bun tops on top of the burgers and enjoy!
Notes
Dairy-Free: to make this dairy-free simply use dairy-free cheese slices and use a plant-based butter.
Gluten-Free: to make this gluten-free simply choose a gluten-free burger bun option.