Place butter, blue cheese, garlic powder, salt, and black pepper in a bowl. Mash butter together with the back of a fork. Transfer butter to a sheet of plastic wrap. Roll plastic wrap around butter to create a cylinder, twisting the ends of the plastic. Refrigerate for at least two hours.
Remove steaks from refrigerator while the grill is prepped. Rub kosher salt into both sides of steak and rest on the counter, lightly covered.
Set up the grill with two zones: direct and indirect cooking. Heat grill to approximately 500 degrees. Oil grates prior to putting the steak on the grill.
Place steak directly over heat without moving for one-fourth the cooking time required to reach the ideal inner temperature. Rotate the steak 90 degrees to create hash marks and cook another one-fourth the cooking time. (Cooking times: Medium-rare - 135 degrees - 4 to 5 minutes per side; Medium - 145 degrees - 5 to 6 minutes per side; Medium-well - 150 degrees - 6 to 7 minutes per side)
Flip the steak and repeat the previous step. If the steak cooks too quickly, move to indirect heating.
Remove from the grill, wrap in aluminum foil, and let rest for at least 5 minutes.
To serve, slice butter and smear over each steak.