01 - Set 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 large bowl.
03 - In a separate bowl, whisk brown sugar, molasses, eggs, melted butter, and vanilla extract until fully blended.
04 - Add wet ingredients to dry and mix until just combined. Fold in nuts and crystallized ginger if desired.
05 - Divide dough in half. With floured hands, form each half into a 12-inch long by 2-inch wide log on the prepared baking sheet.
06 - Bake logs for 25 minutes until firm and lightly golden. Remove from oven and cool for 10 minutes.
07 - Lower oven heat to 325°F for final baking.
08 - Using a serrated knife, cut logs diagonally into 1/2-inch thick slices. Lay slices cut side down on the baking sheet.
09 - Bake slices for 10 to 12 minutes per side, flipping once, until crisp and golden. Transfer to wire rack to cool completely.