Bring oysters and liquor to a simmer in heavy-bottomed pot over medium heat. As soon as oysters are plump, lift them out with slotted spoon and set aside in separate bowl. Bring liquor to a boil.
Meanwhile, roll butter in flour until well-mixed. Add it in bits to boiling liquor, stirring after each addition, until it is all incorporated and liquid begins to thicken. Stir in cream, a good grating of nutmeg, and a liberal grinding of white pepper. Bring to a boil, stirring constantly, and reduce heat to low. Simmer until thickened.
When ready to serve, lift poached oysters from bowl, leaving behind any liquid they may have thrown off, and add to sauce. Let them just heat through, but do not let sauce boil again or oysters will overcook. Remove from heat, taste, and adjust seasonings, adding a pinch or so of salt if needed.
To serve from chafing dish, scald dish with boiling water, dry, and pour in cream oysters. Serve with toast points on the side. To serve as first course, arrange toast points or puff pastry cups on individual plates and ladle oysters and sauce on top.