Step 1

Peel and mince the garlic. Put the garlic in a medium bowl with the butter. Zest or microplane about 1 teaspoon of zest from the lemon into the bowl (remove only the bright yellow zest, leaving the bitter white pith underneath alone). Cut the lemon in half and squeeze about 1 tablespoon of lemon juice into the bowl. Set the remaining lemon aside.

Step 2

Remove the leaves from the parsley stems. Mince the leaves and discard the stems. Add the minced parsley to the bowl. Add the cayenne and black pepper, too. Use a fork to mash everything together and set aside.

Step 3

Shuck the oysters. Discard the top shells and keep the oysters in the deeper bottom shells. Place the shucked oysters on a rimmed baking sheet or in a baking dish (you can fill it with rock salt to help keep the shells steady or use bits of tin foil to the same effect). Dot the butter mixture evenly on the oysters.

Step 4

Heat a broiler. Broil the oysters, about 5 inches from the heat, until the edges of the oysters begin to curl and butter is bubbly, 5 to 7 minutes. Serve hot.