In a large mixing bowl beat butter, cream cheese and flour on low speed until the mixture forms a ball. Divide in half and wrap in plastic wrap and refrigerate for 30 minutes.
On a lightly floured surface roll each portion into a 7-inch circle about 1/8-inch thick. Place one circle on an ungreased sheet pan. Place brie on pastry and top with the remaining pastry circle; pinch edges to seal. In a small mixing bowl beat the egg and water; brush the top and sides of the pastry.
Bake at 400 degrees F for 15-20 minutes or until golden brown. Immediately remove from sheet pan let stand for 30 minutes before serving.