Step 1Melt the butter in a saucepan over medium heat, add the fennel and stir to coat well. Add the wine, cover and cook, stirring occasionally, until the fennel softens almost to a puree and turns a very pale green, 18 to 20 minutes. Remove the lid, increase the heat to high and cook until the liquid evaporates and the fennel begins to sizzle, about 3 minutes.
Step 2In a small saucepan, reduce the cream and minced shallot over medium-low heat until it is just thick enough to lightly coat the back of a spoon, 6 to 7 minutes. Remove from the heat, add the Pernod, and strain into a bowl, discarding the shallot. (Recipe can be prepared to this point and refrigerated several hours in advance.)
Step 3Heat the oven to 450 degrees. Chop the reserved fennel stalks. Scatter the rock salt, fennel seed, chopped stalks and peppercorns on a jellyroll pan. Place the oysters cup-side down on the salt and roast until the shells loosen and just begin to open, 7 to 8 minutes.
Step 4Remove the oysters from the oven and open them, separating the muscle at the top and the bottom and discarding only the flat top shell (save the liquor, oysters and bottom shells separately). Whisk the reserved liquor in with the reduced cream.
Step 5Return the bottom shells with the oysters to the sheet pan on top of the salt. Spoon about 1 tablespoon of the fennel into each of 24 oyster half shells and top each half shell with an oyster. Spoon a generous tablespoon of the reduced cream mixture on top of each oyster, and top each with a sprig of reserved fennel frond. Return the pan to the oven and roast an additional 2 to 3 minutes until the oysters are plump and firm. Remove from the oven and serve immediately.