Place the butter into a bowl. Add in the garlic cloves and kosher salt.
Remove the rosemary leaves from the stalk and chop finely the leaves. Add to the butter and mix until everything is evenly distributed.
Transfer the butter to an approximately 1 foot piece of parchment paper, loosely forming a 6 inch log. Roll the paper lengthwise over the butter to form a log. Using two hands, one on each open end of the paper, twist the ends in opposite directions until the butter inside is tightly wrapped.
Transfer to the freezer for at least one hour or until firmly set. Slice with a knife into rounds, making sure to remove the outer paper!
Heat a cast iron skillet on high until very hot. Add a tablespoon of canola oil and sear the steak for 1 minute and 30 seconds on each side or until a nice brown sear has developed.
In the last minute of cooking, add in 2 slices of compound butter and baste with a spoon (i.e., angle your pan to one side and use the spoon to collect the melted butter and continually pour over the steaks to add flavor).
If there is a fat cap on your steaks, be sure to sear that for about one minute as well.
Let rest on a cutting board for 5 minutes before slicing. Top each steak with one slice of the compound butter to serve.
Strip steak or ribeye: follow recipe (60 minutes cooking time)
If using a filet mignon or sirloin: reduce cooking time to 30 minutes
If using a very large bone-in steak: increase cooking time to 1 hour and 15 minutes
I would not recommend this method for hanger, skirt or flank steak.