Preheat oven to 350 degrees F (175 degrees C). Grease a 6-cup souffle dish.
In a medium saucepan over medium heat, melt the butter. Whisk in the flour, salt, pepper, and dry mustard until blended. Gradually whisk in the milk, and cook, stirring constantly, until mixture thickens.
Remove from heat and stir in the oysters and Parmesan cheese. Beat the egg yolks and stir into the mixture.
In a medium bowl, beat the egg whites until soft peaks form. Gently fold into the oyster mixture. Pour into the prepared souffle dish and bake for 30 minutes, or until puffed and golden.
Sprinkle with the parsley before serving.
Interesting Facts
The souffle is believed to have been invented by the French chef Antonin Careme in the early 1800s.
A souffle is usually made with egg whites whipped into a light foam, which is then folded into a flavoring mixture.
Oyster souffles are a popular dish in French cuisine.