Cool white sauce slightly and flavor well with salt, pepper, nutmeg, then beat in the eggs, one by one.
Line a 15 X 10-inch jelly-roll pan with lightweight aluminum foil.
Butter it and pour in the egg mixture.
Bake at 350 F for 20 minutes or until set but not brown.
Invert on a length of buttered foil and peel off the bottom foil.
Spread with Mushroom Filling and roll up jelly-roll style.
Put on a bake-and-serve platter and wet with butter.
Sprinkle with fine dry bread crumbs.
Before serving, reheat at 325F for about 20 minutes.