Take the salmon out of the fridge 10–15 minutes before cooking so it is not ice cold. Check for pin bones and pull any you feel.
Place the salmon on a plate or board with the skin facing up. Pat the skin very dry with paper towels until it looks dull, not shiny. Flip and lightly pat the flesh side too.
Season the skin with a light, even layer of salt. Turn the fillets over and season the flesh side with the rest of the salt, pepper, and garlic powder if you’re using it. Let the salmon sit like this while you heat the pan.
Set a cast iron or heavy nonstick skillet over medium to medium-high heat. Let it heat for 2–3 minutes. Add the oil and tilt the pan so the bottom is covered in a thin film. The oil should move easily when you swirl it.
Carefully place the salmon in the hot pan, skin side down. Start with the edge closest to you and lay it away from you so the oil doesn’t splash. As soon as the fillet is in, press gently along the top with a flat spatula for 20–30 seconds so the skin makes full contact with the pan.
Let the salmon cook skin side down without moving it for about 5–7 minutes, depending on thickness. You want a steady sizzle. Watch the side of the fish: the color will slowly change from translucent to opaque as it cooks up from the bottom.
When the salmon looks cooked about two-thirds to three-quarters of the way up the side and the skin feels firm, slide a spatula under and flip it onto the flesh side.
Cook on the flesh side for about 1–3 minutes, just until the center is almost opaque but still very moist. If you use a thermometer, aim for about 120–130°F in the thickest part for a medium finish.
If you want a richer taste with the base version, add the tablespoon of butter to the pan in the last minute. Let it melt and gently spoon the buttery juices around the salmon, keeping most of it off the skin so it stays crisp.
Move the salmon to a plate or small rack, skin side up, so steam doesn’t soften the skin. Rest for 3–5 minutes.
Sprinkle fresh herbs over the flesh side. Squeeze lemon over the salmon and serve with your choice of grain and vegetables. Keep any sauce under or beside the fish, not on top of the crispy skin.