How to Make It
Light a grill or preheat the oven to 500°. In a small skillet, toast the fennel seeds over moderately high heat until fragrant, about 1 minute. Transfer to a plate to cool. Pound the seeds to a coarse powder in a mortar. In a bowl, blend the butter with the ground fennel seeds, shallots, fennel fronds, pepper and salt.
Arrange the oysters on the grill, cover and cook for 3 to 5 minutes, just until they start hissing and releasing their juices but are not wide open. Transfer the oysters to a large baking sheet. Alternatively, arrange the oysters on a large rimmed baking sheet and roast in the oven for 3 to 5 minutes, until they start hissing.
Using an oyster knife, pry each oyster open at the hinge, loosen the oyster and discard the flat shell. Top each oyster with 1/2 teaspoon of the fennel butter and serve hot.