Preheat your cast iron skillet over medium heat for 5 minutes.
Pat the salmon completely dry. Season both sides with salt and pepper.
Add the olive oil to the warm skillet, and cook the salmon skin side DOWN for 5 minutes. The skin will release when it is crispy. Flip, and cook for another 1-2 minutes until the salmon has an internal temperature of 120ºF. Remove from the plate and rest it skin side UP so the skin stays crispy. Rest the salmon for 1-2 minutes.
Serve the salmon warm topped with hollandaise sauce.