Preheat the broiler.

Open the oysters, remove them from the shells, and set aside, reserving their liquor.

Strain the liquor (you should have 3⁄4 to 1 cup) to remove any stray pieces of shell. Bring the liquid and shallots to a boil. Continue cooking until reduced by half. Remove the shallots and whisk in the butter. Keep the sauce warm on top of a pan of simmering water or in a double boiler.

Put the oysters back in their shells and place them on a baking sheet filled with coarse salt, which will keep them in place. Sprinkle the oysters with lemon zest, some of the sauce, and season with pepper to taste. Broil until golden, 1 to 2 minutes. Serve immediately with a baguette to soak up the delicious juice.