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1
Heat oven to 350u00b0 F. Butter the bottom and sides of a quarter sheet pan (or 9-inch by 13-inch pan).
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2
Whisk together the flour, cocoa, ginger, and salt in a medium bowl. Set aside.
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3
Using a hand mixer and a large bowl or a stand mixer fitted with the paddle attachment, beat the butter, confectioners' sugar, and dark brown sugar on medium speed until smooth and creamy, about 2 minutes, stopping once or twice to scrape down the sides of your bowl with a rubber spatula. Add the vanilla and beat for a few more seconds. Add the dry ingredients and mix on low speed until the flour has disappeared and the dough is cohesive, about 1 minute; for best texture, don't overmix. Stop the mixer, add the chopped ginger and chocolate, and mix a few more seconds to incorporate.
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4
Turn the dough out into the prepared pan. Using your hands, or a flat-bottomed glass or measuring cup, press the dough to form an even layer.
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5
Score the dough lightly with a knife, marking 4 rows by 5 rows to form 20 squares, and then score each square on the diagonal (or choose another shape). Dock each triangle once with a fork to prevent air bubbles from forming. Sprinkle turbinado sugar generously and evenly over the dough.
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6
Bake for about 30 to 36 minutes, until shortbread is lightly browned all over. The dough's appearance will change from wet/glossy to dry/matte when it's done.
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7
Remove pan from oven and transfer to a cooling rack. While the shortbread is still hot, use a knife to fully cut the shortbread along the lines you scored prior to baking. (Don't wait on this step - cutting the shortbread once it's cooled is messier/crumblier.) Allow shortbread to cool completely in the pan. Once cool, the shortbread bars will break apart very easily. Store in an airtight container for at least two weeks.
