Biscotti are twice-baked cookies, but so worth the time! Use them to dip into fresh coffee, wine or your favorite spirit. Do not skip the orange zest. They can be stored in a tin and they should last up to a week or two.
Preheat oven to 325 degrees. Butter 2 baking sheets. (or use parchment paper).
Beat the sugar and eggs together in a large bowl until blended. Add eggs one at a time, beating well after each. Beat in orange zest and vanilla.
Stir flour, baking powder, cinnamon and salt in a medium bowl. Add dry ingredients to the butter mixture, mix just until incorporated. (I place the wax-paper wrapped dough in the refrigerator for about 10 minutes, just until cool before forming into logs.) This makes them easier to form.
Divide the dough in half. Place each half on the prepared sheet. With lightly floured hands, form each half into a 3-inch wide by 3/4 inch-high log.
Bake until dough logs are firm to touch, about 35 minutes. Remove the logs from the oven and cool 10 minutes.
Transfer logs to a work surface. Using a serrated or sharp knife, cut on diagonal (or straight) into 1/2 -inch thick slices. Arrange cut side down on the baking sheets. Bake until bottoms are golden, about 12 minutes.
Turn Biscotti over, and bake until bottoms are golden, another 12 minutes longer.
Transfer Biscotti to a cooking rack and cool. Can be made 2 weeks ahead. Store in airtight container.