Preheat oven to 375ºF. In large mixing bowl, cream butter and sugar using electric mixer. Add egg yolks; mix and add in flours and extract.
Trim 14-inch Featherweight Decorating Bag to fit No. 1A Tip. Fill bag half-full with cookie mixture. Pipe 1-inch circle of dough on ungreased Baking Sheet spacing 1-inch apart. Using bottom of a glass, gently press to flatten each circle into a disc shape. Sprinkle tops with grated hazelnuts.
Bake 8-10 minutes or until golden brown. Remove from oven. Allow cookies to cool 3 minutes on baking sheet. Transfer cookies to Cooling Grid. Cool completely.
To make filling, place cream, chocolate and butter in 1-quart microwave-safe bowl. Microwave on HIGH 1-2 minutes, stirring every 30 seconds until chocolate is melted. Stir in orange liqueur and orange zest. Refrigerate 30-35 minutes until thickened.
Using Decorating Bag fitted with No. 2A Tip, pipe filling on bottom cookie disc. Place cookie top over filling pressing down gently. Repeat with remaining filling and cookies.