Step 1Shuck the oysters over a bowl, reserving as much of their liquor as possible. Measure the oyster liquor; if you have less than a cup, add enough clam juice to make 1 cup. Set the oysters and the oyster liquor-clam juice mixture aside.
Step 2Melt the butter in a large deep skillet over medium heat. Add the leeks and celery, sprinkle with salt and cook, stirring, until very soft but not browned, about 8 to 10 minutes.
Step 3Whisk in the flour and cook, stirring constantly, 5 minutes. Raise the heat, add the wine and the oyster liquor and/or clam juice and bring to a boil. Boil 2 minutes. Reduce the heat to a simmer and add the cream and milk. Simmer 10 minutes. Add the nutmeg, mace and hot sauce.
Step 4Add the oysters, stir to distribute evenly throughout the liquid and cook just until edges start to curl; do not overcook, about 3 to 4 minutes. Season with more salt, if needed, and pepper to taste and serve at once, ladled over toasted bread.