1.Preheat oven to 350ºF. In a large bowl, mix flour, sugar, baking powder, salt, and cinnamon. With a pastry blender or 2 knives used scissor-fashion, cut in the butter or margarine until mixture resembles fine crumbs.
2.Spoon 1 tablespoon beaten eggs into a cup; reserve. Add chocolate chips, walnuts, vanilla, and remaining beaten eggs to flour mixture; stir until evenly moistened. With hand, knead mixture a few times in bowl until dough forms.
3.On floured surface, with floured hands, divide dough into quarters. Shape each quarter into a 9" by 2" log. Place logs crosswise, 4 inches apart, on 2 large cookie sheets. With a pastry brush, brush tops and sides of logs with reserved egg. Bake logs 25 minutes. Cool logs on cookie sheets on wire rack 10 minutes.
4.Place 1 log on cutting board. With serrated knife, cut warm log crosswise into 1/2-inch-thick diagonal slices. Place slices upright, 1/4-inch apart, on cookie sheets. Repeat with remaining logs. Bake slices 15 minutes to allow biscotti to dry out. Cool completely on sheets on wire racks. (Biscotti will harden as they cool.) Store biscotti in tightly covered container.