01 - Preheat oven to 350°F. Line a 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, beat the softened butter and dark brown sugar with an electric mixer until light and fluffy, about 2 to 3 minutes.
04 - Add molasses to the creamed mixture, then beat in eggs one at a time, followed by the vanilla extract, mixing thoroughly after each addition.
05 - Gradually fold the dry ingredients into the wet ingredients until just combined, avoiding overmixing.
06 - Gently fold in chopped pecans and crystallized ginger if using.
07 - Divide dough in half and shape each portion into a log approximately 10 inches long and 2 inches wide on the prepared baking sheet; flatten slightly.
08 - Bake logs at 350°F for 25 to 28 minutes until firm and lightly browned. Remove and cool 10 to 15 minutes.
09 - Lower oven temperature to 300°F for the second bake.
10 - Using a serrated knife, cut logs diagonally into 1/2-inch thick slices and arrange cut side down on the baking sheet.
11 - Bake slices at 300°F for 10 to 12 minutes per side, flipping halfway through, until dry and crisp.
12 - Transfer biscotti to a wire rack and allow to cool completely before serving or storing.