Place the butter in a cast iron skillet and let it melt. You want the butter melted and the skillet hot for the next step.
Carefully remove the top round roast from the bag. It might want to fall apart and you do not want that to happen.
Place the top round roast, seasoning side down in the cast iron skillet and sear. This normally takes 2 to 3 minutes.
Turn the top round roast over and sear the other side.
Remove the top round roast, allow it to sit on a plate with a foil tent for 10 minutes.
Cut and serve.
Note: I did use a semi-frozen top round roast. The time and temperature would be the same even if it was thawed completely. I also used the drippings in the bag to make a gravy once the searing of the meat was done. This is an optional step.