1/2 c plus 2 tbsps semidry white wine, preferably Sémillion
1 dozen Bluepoint or other good-sized oysters such as Cape Cod, scrubbed
2 tbsps unsalted butter
1/2 c water
1 large egg yolk
Salt & freshly ground pepper
1/4 c heavy cream
1/4 tsp (packed) saffron threads
Directions
Step #1 In a large saucepan, mix 1/2 c of the wine with the water & bring to a boil over high heat.
Step #2 Using tongs, cover & steam until they start to open, add the oysters to the saucepan in a single layer, about 3 mins.
Step #3 Using tongs, transfer the oysters to a plate as they open.
Step #4 Reserve the cooking liquid; you should have about 1/2 c.
Step #5 Remove the oysters from their shells, put them in a bowl & cover with a damp paper towel.
Step #6 Reserve 12 concave shells.
Step #7 Melt 1 tbsp of the butter in a medium saucepan.
Step #8 Add the leeks, crumble in the saffron & stir.
Step #9 Cook over low heat/flame until the leeks soften, about 8 mins.
Step #10 Slowly add the reserved oyster liquid, stopping before you reach the grit at the bottom, & cook over moderate heat until the liquid is almost evaporated, about 3 mins.
Step #11 Add the heavy cream & the remaining 2 tbsps of white wine & let simmer until the sauce is thickened, about 3 mins.
Step #12 Spice up with salt & pepper.
Step #13 Preheat the broiler.
Step #14 Arrange the 12 oyster shells on a rimmed baking sheet or in a shallow baking dish.
Step #15 Using a fork, divide the sautéed leeks among the shells.
Step #16 Set an oyster on the leeks in each shell & stir any accumulated oyster juices into the sauce.
Step #17 Melt the remaining 1 tbsp of butter.
Step #18 Whisk the egg yolk & the melted butter into the cream sauce & spoon the sauce over the oysters.
Step #19 Broil as close to the heat as possible for about 45 seconds, just until the sauce is bubbling & the oysters are lightly glazed.
Step #20 Serve at once.
Step #21 Make Ahead: The recipe can be prepared through Step 3 up to I hr ahead; let this stand at about room temp.