The flavorful parsley butter in this recipe works triple time. First, it slowly melts into the oysters, helping to cook them and keep them juicy. It also melts into the pan, helping to crisp up the bread. Lastly, it becomes an herby sauce that is dumped onto the toasty bread for a delicious appetizer.
Puree the butter, parsley, garlic, lemon zest, 1/4 teaspoon salt and a few grinds of pepper in a food processor until smooth and bright green from the parsley, about 1 minute.
Line a 12-inch cast-iron skillet with the baguette slices. Open the oysters with an oyster knife, detach the oyster from the bottom shells and discard the top shells. Place one oyster half onto each baguette slice and top each with a heaping teaspoon of the parsley butter.
Roast the oysters until the parsley butter is melted and the baguette slices are lightly toasted, 8 to 10 minutes. To serve, pour an oyster and the butter from the shell onto each baguette slice and eat immediately.