01 - Preheat oven to 350°F. Line a baking sheet with parchment paper.
02 - Whisk together flour, ground ginger, cinnamon, cloves, nutmeg, baking powder, and salt in a medium bowl.
03 - In a large bowl, cream butter and brown sugar until light and fluffy. Beat in eggs one at a time, then mix in molasses and vanilla extract.
04 - Gradually add dry ingredients to the wet mixture, stirring until just combined. Fold in nuts and crystallized ginger if desired.
05 - Divide dough in half. On the prepared baking sheet, shape each portion into a log approximately 12 inches long and 2 inches wide, slightly flattening the tops.
06 - Bake logs for 25 to 28 minutes until firm and lightly golden. Cool on the pan for 10 minutes.
07 - Reduce oven temperature to 300°F.
08 - Using a serrated knife, cut logs diagonally into 1/2-inch thick slices. Arrange slices cut-side down on the baking sheet.
09 - Bake slices for 10 to 12 minutes per side until crisp and dry. Cool completely on a wire rack.