1 cup all purpose flour
1/2 teaspoon baking powder
1/4 teaspoon salt
1/2 cup (1 stick) unsalted butter, room temperature
1/3 cup sugar
1/2 cup finely ground husked toasted hazelnuts (about 2 ounces)
1 teaspoon vanilla extract
4 ounces high-quality milk chocolate (such as Lindt or Perugina), chopped
1/3 cup coarsely chopped husked toasted hazelnuts
Position rack in center of oven and preheat to 325°F. Line large baking sheet with parchment paper. Whisk flour, baking powder, and salt in medium bowl to blend. Using electric mixer, beat butter and sugar in large bowl until smooth. Beat in 1/2 cup finely ground hazelnuts and vanilla. Beat in flour mixture until just combined.
Shape dough by tablespoonfuls into 3-inch-long logs. Place on prepared baking sheet, spacing 1 inch apart. Bake cookies until light golden brown around edges, about 20 minutes. Cool on baking sheet 5 minutes. Transfer to rack; cool cookies completely.
Stir milk chocolate in top of double boiler over barely simmering water until melted and smooth. Remove from over water. Place 1/3 cup coarsely chopped hazelnuts in small bowl. Dip 1 end of cookie into melted chocolate, then into coarsely chopped hazelnuts. Return to rack. Repeat with remaining cookies. Let stand until chocolate is set, about 1 hour. (Cookies can be made 2 days ahead. Store in airtight container at room temperature.)