In the bowl of an electric mixer, fitted with a paddle attachment, blend the flour, the sugar, the baking soda and the salt until the mixture is combined well
In a small bowl whisk together the whole eggs, the yolk, the vanilla and the zest, add the mixture to the flour mixture, beating until a dough is formed and stir in the almonds
Turn the dough out onto a lightly floured surface, knead it several times and halve it
Working on a large buttered and floured baking sheet, with floured hands form each piece of dough into a flattish log 12 inches long and 2 inches wide, arrange the logs at least 3 inches apart on the sheet, and brush them with the egg wash
Bake the logs in the middle of a preheated 300 degree F for 50 minutes and them cool on the baking rack for 10 minutes
On a cutting board, cut the logs crosswise on the diagonal into 1/2 inch thick slices, arrange the biscotti, cut sides down, on the baking sheet and bake them, in the 300 degree F oven for 15 minutes on each side
Transfer the biscotti to racks to cool and store them in airtight containers.
