Chop mushrooms and onion. Warm sherry, olive oil and garlic in fry pan. Add mushrooms and onion and saute for five minutes to blend. Cool for 10 minutes in pan.
In a large bowl, mix sour cream, yogurt, mustard and parsley. Add mushroom saute (with juices) to bowl and mix well. Refrigerate for 30 minutes (over night is fine). For an extra zing add some cayenne to the sour cream mixture.
Grease two large baking dishes (9" x 13").
Lay out crepes, add a sprinkle of brie cheese to the middle of each crepe. Spoon 2 tbls of mushroom mixture on top of cheese and roll. Place rolled crepes in baking dish, side by side. Once all crepes are completed, sprinkle top with cayenne and paprika.
Bake at 350 for 15 - 20 minutes. Serves 10, with 2 crepes each.