Preheat the oven to 325 degrees F. Line a baking sheet with parchment paper.
Mix the flour, sugar, baking soda and salt with an electric mixer in a medium bowl. Add the eggs, 1 at a time, scraping down the bowl after each addition. Add the extract, orange zest and almonds, mixing to make a somewhat sticky dough.
Turn the dough out onto a floured board and knead just until it comes together. Halve the dough and shape into 2 logs, approximately 12 by 2 inches. Transfer the logs the prepared pan, spacing them about 3 inches apart. Brush the dough all over with the beaten egg and sprinkle with sanding sugar, if desired. Bake until they are firm and golden in color, about 45 minutes. Transfer the logs with a metal spatula to a cutting board and cool for a few minutes.
Cut the logs with a serrated knife on an angle into 1/2-inch slices. Lay them cut side down on the pan. Return to the oven and bake until golden brown on 1 side, about 10 minutes. Remove from oven, flip biscotti and continue to bake until golden, about 10 minutes more. Transfer to a rack to cool.
Store biscotti for up to 2 weeks in an airtight container.
Cook's Note: These biscotti are traditional and very crunchy. They are made for dunking.