Preheat the oven to 350 degrees F. Combine the flour, salt, baking powder, espresso powder, and cinnamon. Set aside.
In a mixing bowl, cream the butter and sugar together until fluffy. Scrape down the sides and add the eggs and vanilla. Beat until combined.
Combine half of the flour mixture, then mix in the other half. Fold in the chocolate chips.
Scoop half the dough onto one side of the prepared pan and, using wet hands, pat it into a 10-inch x 2-inch rectangle, about 1 inch thick. Repeat with the remaining dough.
Bake for 20 to 30 minutes, until the logs are set. Remove from the oven and let cool for 25 to 30 minutes. Reduce the oven temperature to 325°F.
Carefully transfer the logs to a cutting board. Use a serrated knife to slice the biscotti diagonally, about ½ to ¾ inch wide. Draw the knife back and forth through the logs rather than pressing down to help prevent crumbling.
Return the slices to the baking sheet, standing them upright with about ½ inch between each. Bake for another 25 to 30 minutes, until dry and crisp. Remove from the oven and transfer to a wire rack to cool completely.
Dip or drizzle the cooled biscotti with melted chocolate, if desired. Allow the chocolate to set before serving.