01 - Preheat oven to 350°F. Line a large baking sheet with parchment paper.
02 - In a medium bowl, whisk together flour, ground ginger, cinnamon, cloves, nutmeg, baking powder, baking soda, and salt.
03 - In a large bowl, cream softened butter and brown sugar until light and fluffy. Beat in eggs one at a time, then add molasses and vanilla extract, mixing until combined.
04 - Gradually add dry ingredients to the wet mixture, mixing just until incorporated. Fold in nuts and crystallized ginger if using.
05 - Divide dough into two equal parts. With floured hands, shape each into a log approximately 12 inches long and 2 inches wide on the prepared baking sheet. Slightly flatten each log.
06 - Bake logs for 25 to 28 minutes until firm and lightly browned. Remove from oven and cool on baking sheet for 10 minutes.
07 - Reduce oven temperature to 325°F.
08 - Using a sharp serrated knife, slice logs diagonally into 1/2-inch thick pieces. Arrange slices cut side down on the baking sheet.
09 - Bake slices for 10 minutes, then flip and bake an additional 10 to 12 minutes until crisp and golden.
10 - Cool biscotti completely on a wire rack before storing in an airtight container.