For crust, in a medium bowl, combine the 1 C. flour, the 1/2 C. sugar, the cocoa powder, and baking powder. Cut in butter until mixture resembles fine crumbs. Stir in ground hazelnuts. Separate 1 of the eggs; set aside egg white to use in filling. Stir yolk and vanilla into cocoa powder mixture. Press mixture into bottom of an ungreased 9x9x2 inch baking pan. Bake in a 325°F oven for 15 minutes. Meanwhile, for filling, in a medium bowl, combine cream cheese, sour cream, the 1/3 C. sugar, hazelnut liqueur or milk, the 1 Tbs. flour, orange flavoring (if desired), the egg white, and remaining egg; beat with an electric mixer on low to medium speed until smooth. Stir in orange peel. Spread over crust in pan. Bake in the 325°F oven for 25 to 30 minutes or until set. Cool on wire rack. Chill thoroughly. To serve, drizzle with chocolate syrup and top with chopped hazelnuts, if desired.

Makes 12 servings.