Combine all the ingredients for the blackening seasoning in a bowl and whisk it well. Set aside.
Melt butter and set it aside as well.
Pat salmon fillets dry with a paper towel.
Set a large skillet (or another pan you with to use) on the stove over medium heat or just a little below medium heat. (Every stove is different especially comparing gas and electric, so you will know your stove best. Just don’t set the heat higher than medium.) It will take about 5 minutes to preheat the skillet.
While the pan is preheating, season the salmon. Brush each salmon fillet with butter on top and sides and dip into the seasoning on top and the sides.
Spread oil in the preheated pan all over the bottom.
Place seasoned salmon into the pan flesh down and let it cook for 3-4 minutes.
Flip each filet skin side down and let it cook for 5-6 more minutes. (Thick fillets may take another minute or so.)
Take salmon out of the pan, let it rest for 5 minutes, and serve with lime wedges.
How to tell if salmon is cooked:
Total cook time will always depend on the thickness of salmon fillets. Salmon is considered fully cooked at 145° internal temperature but many people find it too well done. Personally, I prefer salmon at either medium or medium-well temperature, which is around 125°-130°.
You can also tell if salmon is done by touch. When meat is cooked through, it will be firm to the touch when pressed in the center. If you still feel some squishy texture inside, it’s not cooked through.
Another way to tell is to gently press on the flesh, on top, and slightly pull it apart, it should flake easily.