* Heat olive oil in a large skillet over high heat until hot. Add shallots and sautéuntil translucent.
* Add mushrooms and continue cooking for 10 minutes, stirring occasionally.
* Season with sherry, salt and pepper. Reserve and let cool.
* Cut cheese in half through the middle to form a top and bottom layer.
* Place mushroom filling on bottom half and cover with top. Wrap tightly with plastic wrap and freeze for 30 minutes. Roll out pastry to a 12" square.
* Place Brie in the center of the dough and gather up the edges as evenly as possible to encase the cheese completely.
* Form a bundle with the excess dough at the top. Tie with cotton twine to hold together.
* Brush beaten egg on pastry and bake in a 375°F. oven for 20 minutes.
* Serve with crackers or crusty bread.