Step 1: Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides to easily lift the bars out later. Lightly grease the parchment paper.
Step 2: In a medium bowl, whisk together the all-purpose flour, baking soda, ground ginger, ground cinnamon, ground allspice, ground cloves, ground nutmeg, ground black pepper, and salt. Set aside.
Step 3: In a large bowl, combine the melted unsalted butter, packed brown sugar, and granulated sugar. Whisk until well combined.
Step 4: Stir in the unsulphured molasses, large egg, and pure vanilla extract until the mixture is smooth and fully incorporated.
Step 5: Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed with an electric mixer or by hand with a spatula until just combined. Be careful not to overmix; a few streaks of flour are fine.
Step 6: Spread the thick batter evenly into the prepared 9x13 inch baking pan. Use an offset spatula or the back of a spoon to smooth the top.
Step 7: Bake for 25-30 minutes, or until the edges are lightly golden and a toothpick inserted into the center comes out with moist crumbs attached (not wet batter). The center should look set.
Step 8: Remove from the oven and let the bars cool completely in the pan on a wire rack before lifting them out using the parchment paper overhang. Once fully cooled, slice into 16 squares and enjoy!