These crunchy breakfast cookies will keep for up to a month.
Heat oven to 325 degrees. Lightly oil and flour a large baking sheet or line it with parchment paper.
In a mixing bowl, whisk together flour, cornmeal, sugar, lemon zest, baking powder, and salt until well blended.
In a small bowl, whisk together 1/2 cup water, the eggs, and the vanilla and stir into the flour mixture; the dough will be sticky. Stir in hazelnuts and raisins.
Divide the dough into 3 equal portions. On a heavily floured work surface, shape each portion into a log about 13 inches long by 2 inches wide. Place the logs 2 inches apart on the prepared baking sheet. Bake until logs are firm and golden brown on the bottom, about 45 minutes. Remove logs from the baking sheet and cool on a wire rack for at least 30 minutes.
With a clean serrated knife, cut each log into 1/2-inch-thick diagonal slices. Place the slices in a single layer on a clean baking sheet (you'll probably need to use 2 baking sheets). Bake until tops of biscotti are golden brown, about 15 minutes. Turn biscotti over and bake until golden brown and very dry, about 15 minutes more. Cool the biscotti completely on a wire rack before serving. Store in an airtight container.