1 cup Hazelnuts
1/2 cup Butter, sweet
1 cup Sugar
1 tsp Vanilla extract
2 cup Flour, plus 2 tbsp
1 tsp Baking powder
1/4 tsp Salt
Preheat oven to 350 F. Spread the hazelnuts on a baking sheet and toast in the oven for 8 to 10 minutes, until fragrant. Place the nuts in a dish towel and rub them together to remove some of the skin. Coarsely chop the hazelnuts and set aside.
In a large bowl, using a hand-held electric mixer, beat the butter at medium speed until soft and creamy. Add the sugar and lemon zest and beat until the mixture is very light and fluffy, about 2 minutes. Beat in the eggs, one at a time, and then beat in the vanilla.
In a medium bowl, toss the flour, baking powder and salt. Gradually add the flour mixture to the butter, beating on low speed until a smooth dough forms. Using a wooden spoon, work in the hazelnuts until evenly distributed.
Divide the dough in half in the bowl. With lightly floured hands, form the dough into two 10-by-2 inch rectangular logs. Place the logs on an ungreased baking sheet, at least 2 inches apart. Bake for 30 minutes, or until the logs are set and golden brown. Remove from the oven and let cool on the baking sheet for 15 minutes.
Using a serrated knife and a sawing motion, carefully cut the logs into 1/2-inch diagonal slices. discard the end pieces. Arrange the slices, cut sides down and close together, on 2 baking sheets. Bake the biscotti on the top and middle racks of the oven for 8 to 9 minutes, or until lightly browned. Turn the biscotti over, switch the position of the baking sheets and continue baking until lightly browned on the other side, about 9 minutes longer. Let the biscotti cool completely on the baking sheets.