Melt butter or margarine in a frying pan; add the shrimp and onion, and sauté for about 3 minutes. Do not brown.
Sprinkle a little flour at a time into the mixture. Add a little milk slowly, continuously stirring to avoid lumps. Add mustard, nutmeg, salt and pepper, and cook for 3 to 5 minutes. Stir in the cream cheese(cut into thin slices) until it is completely blended, then warm through, but do not boil.
Serve with cooked rice or noodles. Cooking and prep times are approximate. The recipe didn't say.