Preheat Blackstone to high heat.
In a small bowl mix together the rub ingredients and set aside.
Place the filets on a cutting board and pat them dry with a paper towel.
Melt 3 Tablespoons of the butter in a bowl. Using the basting brush, brush the melted butter on the fish filets and then sprinkle the Blackened Rub on the filet. Flip the filet over and repeat on the other side.
Once Blackstone is preheated, melt the remaining 3 Tablespoons of butter on the cooking surface.
Place the fish on the Blackstone in the melted butter. After a few seconds, you can grab your halved lemon and squeeze the juices right onto the filet.
Once there is a good char on the filet, about 2-3 minutes, flip it over to cook the other side. Cook for another 2-3 min or until your fish is done, it will be flaky when it is done cooking.
Pull off the Blackstone, rest for a few minutes, and serve.