1Heat oven to 375°F. In medium bowl, beat cookie ingredients with electric mixer on medium speed 30 seconds or until mixture looks like coarse crumbs. Mix with hands until soft dough forms.
2On lightly floured surface, roll dough to 1/4-inch thickness. (If dough is too sticky to roll out, cover and refrigerate 15 minutes.) Cut with floured 1 3/4-inch fluted cookie cutter. On ungreased cookie sheets, place cutouts 2 inches apart.
3Bake 8 to 9 minutes or until edges are set. Cool 1 minute; remove from cookie sheets to cooling racks. Cool completely, about 10 minutes.
4In large bowl, beat 1/2 cup butter, the powdered sugar and vanilla with electric mixer on medium speed until light and fluffy. For each sandwich cookie, spread slightly less than 1 tablespoon filling on bottom of 1 cookie. Top with second cookie, bottom side down; gently press together. Sprinkle crystallized ginger on edges of filling.