FOR COOKIE CRUST:
PREHEAT oven to 350° F.
BEAT flour, butter, granulated sugar, baking powder and cinnamon in large mixer bowl until crumbly. Stir in nuts. Press onto bottom of ungreased 13 x 9-inch baking pan. Bake for 15 to 18 minutes or until firm.
FOR CHOCOLATE LAYER:
MELT morsels and butter in medium, heavy-duty saucepan over lowest possible heat; stir until smooth. Remove from heat; stir in brown sugar, eggs and vanilla extract. Pour over hot crust. Bake for 20 to 25 minutes or until center is set. Cool in pan on wire rack. Sprinkle with powdered sugar.