Preheat oven to 325ºF. Lightly spray or grease 2 baking sheets.
Using an electric mixer, beat butter and sugar in a large bowl, until smooth. Beat in ½ cup hazelnuts and vanilla, beat in flour and baking powder until combined.
Drop dough onto prepared pans by tablespoons spreading to make a 3x1” stick, spacing 2” apart on pan. Bake cookies for 18-20 minutes, or until edges are golden brown. Remove to wire racks to cool.
In the top of a double boiler melt the chocolate until smooth. Spread 1/3 cup of hazelnuts on a small dish. Dip 1 end of the cookie into melted chocolate, then into hazelnuts. Return to rack to cool, Repeat with remaining cookies.