Preheat oven to 350°.
Place hazelnuts on a baking sheet. Bake at 350° for 12 minutes or until toasted, stirring once. Turn nuts out onto a towel. Roll up towel; rub off skins. Finely chop nuts.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients in a large bowl; stir in 6 tablespoons hazelnuts. Combine 2 eggs and vanilla in a small bowl; stir with a whisk until well blended. Add egg mixture to flour mixture (mixture will be very crumbly).
Knead dough in bowl with wet hands until dry ingredients are moist. Turn dough out onto a baking sheet coated with cooking spray. Shape dough into 2 (14 x 1 1/2-inch) logs. Combine water and egg white; brush evenly over logs, and sprinkle with remaining 2 tablespoons nuts. Bake at 350° for 24 minutes.
Reduce oven temperature to 300°. Cut logs diagonally into 1/4-inch-thick slices with a serrated knife. Carefully stand cookies on edge on ungreased baking sheets. Bake at 300° for 30 minutes or until dry but not browned. Remove cookies from pans; cool on wire racks.
Place chocolate in a small, shallow dish. Microwave at HIGH 30 seconds or until almost melted, stirring until smooth. Dip 1 side of each cookie lightly in chocolate to coat in a thin layer, shaking gently to remove excess chocolate. Place cookies on wax paper; let chocolate dry for at least 2 hours.