There is much ado over the original recipe for Oysters Rockefeller. We do know that is was invented by Jules Alciatore, the second-generation proprietor of Antoine's restaurant in New Orleans. We don't know, however, what exactly went into the original dish—just that there was a wealth of bright green herbs and it was rich, like John D. Rockefeller himself.
If you can't go to the famous restaurant to have the original recipe. . Here's an easy version of the recipe :
3 dozen fresh oysters ( washed/ open & save bottom shell for serving)
1 onion finely chopped
1/2 C Butter cubed
1 pkg fresh spinach torn
1 C Romano cheese (grated)
1 T lemon juice
1/8 t peper
Kosher Salt to hold oysters.
* The original recipe has many variations : like adding 1/2 teaspoon Herbsaint or Pernod**, made with watercress ,fennel and parsley. . https://whatscookingamerica.net/Seafood/OystersRockefeller.htm