01 - Preheat oven to 350°F. Line a large baking sheet with parchment paper.
02 - Whisk together flour, ground ginger, cinnamon, cloves, nutmeg, baking powder, baking soda, and salt in a medium bowl.
03 - Using an electric mixer, beat butter and brown sugar until light and fluffy. Add eggs one at a time, beating after each addition. Mix in molasses and vanilla extract until combined.
04 - Gradually add dry ingredients to the wet mixture, stirring just until combined. Fold in chopped nuts and crystallized ginger if using.
05 - Divide dough into two equal portions. On the prepared baking sheet, shape each portion into a 12-inch long and 2-inch wide log using floured hands, slightly flattening the tops.
06 - Bake logs at 350°F for 25 to 28 minutes until firm and lightly browned. Remove and cool on the sheet for 10 minutes.
07 - Lower 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 biscotti for 10 minutes, flip, and bake an additional 10 to 12 minutes until crisp and golden.
10 - Allow biscotti to cool completely on a wire rack before storing.