Preheat the oven to 350 degrees F. Prepare a baking sheet with a very light coating of oil.
Sift the flour, baking powder, salt, and sugar into a mixing bowl. In a separate bowl, lightly beat together the eggs and the egg white and add them to the flour mixture. Stir in the lemon peel and anise seeds, mixing just until the dough is smooth.
Using floured hands, scoop half of the dough out of the bowl and onto one side of the baking sheet. Shape it into a 15-inch log. Make a second log on the other side of the sheet with the remaining dough. Space the logs at least 6 inches apart.
Bake for 25 to 30 minutes, until the top of each biscotti log is firm. Remove them with a long spatula to a wire rack and cool for 10 to 15 minutes.
Cut each log on a diagonal into about twenty 1/2-inch-thick slices and place the slices, cut side down, on the baking sheet. Reduce the temperature to 325 degrees F and bake for 15 minutes. Allow them to cool completely.