1. Whisk the eggs with the sugar until the mixture is pale. Add the vanilla, salt, butter, and zest.
2. In a large bowl, sift the flour and baking powder.
3. Add the egg-sugar mixture to the flour and mix well. Add the lemon juice and almonds.
4. Divide the dough into 2 pieces. Wrap each piece in plastic wrap. Refrigerate for 1 hour.
5. Preheat the oven to 350°F.
6. On a lightly floured surface, knead each ball of dough for 1 minute. Roll out the dough into an oval shape with your hands.
7. Place on a buttered cookie sheet and bake. Cook for about 15 to 20 minutes.
8. Remove from the oven and let cool on a rack. When cooled, with a bread knife, cut each cake into equal slices. Place these slices on a baking sheet and put in the oven at 300°F for about 15 minutes.
9. Remove from the oven; place the biscottis on a rack and let cool completely.