Preheat oven to 325°F (160°C). Spread hazelnuts on baking sheet. Bake 6 to 8 min. or until fragrant and skins are blistered. Cool slightly then wrap in clean tea towel and rub to remove skins. Place nuts in food processor. Pulse to a fine meal. Set aside. Increase oven temperature to 350˚F (180˚C).
In bowl, beat egg whites with hand mixer until soft peaks form. Gradually, beat in sugar to stiff glossy peaks. Beat in vanilla. Fold in ground hazelnuts until just combined.
Drop batter by tablespoonfuls on parchment paper-lined baking sheets, 2-in. (5-cm) apart. Bake 18 to 20 min., or until firm to the touch and lightly golden.
Remove from oven. Let stand on baking sheet 5 min. before transferring cookies to rack to cool completely. Store in airtight container up to 1 week.
Drizzle with melted chocolate or sandwich chocolate hazelnut spread between two cookies to make hazelnut sandwich cookies.