Pat the fresh cod fillets dry using a clean paper towel to ensure a perfect sear. Season both sides generously with kosher salt, freshly ground black pepper, and your choice of chopped fresh herbs, such as dill or parsley.

Heat 2 tablespoons of olive oil in a large cast-iron skillet over medium-high heat. Wait until the oil is shimmering, about 2 minutes. Carefully add the seasoned cod fillets and let them cook undisturbed for 4-5 minutes.

Gently flip each fillet using a spatula and continue cooking on the other side for another 4-5 minutes. Once cooked perfectly, remove the fillets from the skillet and set them aside.

Reduce the heat to medium and add 4 tablespoons of unsalted butter to the same skillet. Once melted, stir in the freshly squeezed juice of one lemon along with any remaining chopped herbs. Let the sauce simmer for about 1-2 minutes.

Return the cooked cod fillets to the skillet, gently spooning the lemon butter sauce over them. Cook together for an additional minute to warm the cod through, then transfer to serving plates.