Preheat the oven to 350ºF (175ºC.) Line a baking sheet with parchment paper or a silicone baking mat.
In a large bowl, whisk together the flour, cornmeal, sugar, baking soda, and salt.
In a separate bowl, mix together the eggs, lemon zest, and vanilla or almond extract. Make a well in the center of the flour mixture and pour in the beaten eggs. Add the butter, then mix until the dough is wet and crumbly. Add the nuts and stir to get them mixed well into the dough.
Turn the dough out onto a lightly floured counter and knead a few times until smooth. Divide the dough in two, and roll each portion into a 13-inch (33cm) long, then transfer them to the baking sheet. Leave ample space between the two logs as the dough will spread a bit during baking.
Bake the logs for 20 minutes, or until they feel set. Remove them from the oven and let cool for 20 minutes. Reduce the heat of the oven to 250ºF (120ºC.)
Using a sharp bread knife, slice the longs crosswise into individual cookies, each about 1/3-inch (1cm.) Place the biscotti on the baking sheet, cut side down, and bake for 20 minutes. Remove the biscotti from the oven and turn each one over, then continue to cook for 10 to 20 minutes more, until golden brown.
Let cookies cool completely, then store in an airtight container. These biscotti will keep for at least two weeks.