Flavor the Butter

Grate 1 tsp of zest from the lime into a small bowl, and then halve the lime and squeeze the juice (from both halves) into the bowl. Add the butter, cilantro, and garlic, and stir to blend. Set aside.

Cook the Tilapia

Heat the oil in a large cast-iron skillet or sauté pan over high heat. Rub the tilapia all over with the blackening seasoning. When the oil in the pan starts to lightly smoke, add the fish and cook undisturbed until the spice rub becomes dark and crusty, 3-4 minutes. Flip and cook until the fillets flake with gentle pressure from your finger, 1-2 minutes more.

Finish the Dish

Transfer the fish to four serving plates and immediately top each with a bit of the flavored butter.