Preheat oven to 350° F. Line a baking sheet with a silicone baking mat or parchment. Set aside.

Combine flour and 2 cups powdered sugar in medium bowl. Grate chocolate over bowl and stir to combine. Place shortening in large mixer bowl; beat at medium speed, adding flour mixture gradually until combined. Add vanilla extract; beat until combined. Freeze for 10 minutes.

Roll 1 tablespoon dough into ball; repeat with remaining dough. Place balls 1-inch apart on ungreased baking sheets and press lightly to flatten.

Bake for 16 to 18 minutes. Cool on baking sheets for 1 minute; remove to wire racks to cool completely. Dust with remaining 1/4 cup powdered sugar.