Brown beef slices in butter on <a href="http://amzn.to/1MkWOe0" target="_blank">cast iron</a> on medium-high heat. Flip after 1 minute of cooking time or when golden-brown and cook on the other side.
Take the slices off the pan and arrange on plate.
Top with sliced red onions and chopped fresh dill.
Season with <a href="http://amzn.to/1QCa9Kt" target="_blank">sea salt</a> and squeeze lemon juice.
Enjoy immediately or wait for the flavors to mingle. Either way it's a delicious treat.