I just made this recipe once, and I substituted toasted sliced almonds for the hazelnuts. It was really good.
1.
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.
2.
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.
3.
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.
4.
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.
5.
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.
