Cut onion in half and then slice.
Mix ground beef with Worcestershire sauce, salt and pepper. Form into 4 patties and set aside.
Butter both sides of your bread slices.
Melt 2 tablespoons of butter in a skillet at med-low heat. Add onion. Cook for about 20-25 min stirring occasionally until softened and browned.
While onions are cooking, place a large skillet over medium heat. Toast bread in the pan on both sides.
In the large skillet, melt 2 tablespoons of butter at medium heat. Cook burgers for about 3-4 min on one side and flip. Continue cooking until done (140F for medium) usually another 3-5 minutes.
Once nearly done add cheese to burger. Cover to melt.
Stack up your burgers and enjoy!