Preheat oven to 350 degrees. Warm a souffle dish and butter well. Melt 2/3 of the butter in a saucepan, add onion and garlic and saute until soft. Add flour and stir well, add dried mushrooms and water they soaked in, stir well and add milk and salt and pepper to taste.

Cook Oyster mushrooms separately in remaining butter, saute until soft and add to the mixture; allow to cool. Mix in beaten egg yolk. Whisk egg whites until stiff and fold into mixture. Put mixture in well-buttered souffle dish and cook in preheated oven for 28 minutes. The middle should be quite soft. Serve immediately.