Before cooking blackened shrimp, remove the shell and devein the shrimp. If you are serving them as an appetizer, leave the tail on. But if you will enjoy them as a main dish, remove the tail as well. Then, pat the shrimp dry with a paper towel and put them into a mixing bowl.
In another small bowl, mix together the spices and herbs for the blackening seasoning.
Toss the shrimp with 4 tbsp of melted butter and then with the seasoning blend.
Preheat a large cast-iron skillet over medium-high heat. Add the oil (make sure it sizzles) and 2 tbsp of butter. Let the butter melt and make sure the grease sizzles. Then add the shrimp in one even layer. If needed, cook them in batches!
Cook shrimp until pink and opaque on one side, about 1-2 minutes. Then, flip to the other side and cook for an additional 1-2 minutes. The time will depend on the size of the shrimp!
Take them out of the pan as soon as they're fully cooked. Serve with lime wedges and chopped parsley as an appetizer or over grits, creamy polenta, zoodles, or pasta.