1. In a large bowl, cream together the butter and sugar. Add eggs, vanilla and liqueur; blend well.
2. In a separate bowl, combine the flour, salt and baking powder. Add the hazelnuts to the egg mixture, then add the flour and stir until just blended.
3. On a floured surface, roll the dough into a cylinder 1-3/4" in diameter by 12".
4. Place the dough on a cookie sheet and bake in 325 degree oven for about 25 minutes. Allow to cool for 5 minutes.
5. Diagonally slice the roll into 1/2-inch cookies, and place face side up on the cookie sheet. Bake for 10 minutes. Allow to cool overnight.
Serve with espresso or a full-bodied red wine.