Let dough stand at room temperature 10 minutes to soften. Meanwhile, heat oven to 350°F. In food processor with metal blade, process hazelnuts with on/off pulses until finely ground.
In large bowl, stir or knead cookie dough, flour, ground nuts and vanilla until well blended. Divide dough in half. On lightly floured surface, roll each half to 1/4-inch thickness. Cut dough with 2-inch scalloped or round cookie cutter; place 2 inches apart on ungreased cookie sheets.
Bake 9 to 11 minutes or until edges are golden brown. Cool 1 minute; remove from cookie sheets to cooling racks. Cool completely, about 20 minutes.
To make each sandwich cookie, spread 2 teaspoons hazelnut spread on bottom of 1 cookie. Top with second cookie, bottom side down; gently press cookies together.
Place remaining hazelnut spread in resealable food-storage plastic bag; seal bag. Cut small tip from corner of bag; drizzle spread over cookies. Store between sheets of waxed paper in tightly covered container.