Double Dark-Chocolate and Ginger Biscotti

1 cup all-purpose flour, spooned and leveled
1/3 cup unsweetened cocoa powder
1 1/2 teaspoons baking powder
1/4 teaspoon salt
1 large egg, plus 1 large egg yolk
1/2 cup sugar
1 teaspoon vanilla extract
1/4 cup canola oil
1/2 cup walnuts, coarsely chopped
3 ounces dark chocolate*, coarsely chopped (1/2 cup)
1/4 cup finely chopped crystallized ginger

*Avoid getting water in the chocolate mixture

Preheat oven to 350 degrees. Line a large baking sheet with parchment paper.

In a medium bowl, whisk together flour, cocoa powder, baking powder, and salt until well combined; set aside. In the large bowl of an electric mixer, beat egg, egg yolk, and sugar until light and fluffy; beat in the vanilla and oil until well combined.

With the mixer on low, beat in dry ingredients until combined. Fold in walnuts, chocolate, and ginger with a rubber spatula (dough will be stiff).

With moistened hands shape the dough into 2 logs, each about 9 inches long and 2 1/2 inches wide. Bake until set on top, about 20 minutes. Cool 10 minutes in pan. Reduce oven temperature to 325 degrees.

Transfer logs to a cutting board and, with a serrated knife, cut each log on the diagonal into 16 slices, each 1/2 inch thick. Bake until crisp, about 20 minutes, turning the biscotti over midway through. Cool 5 minutes on a baking sheet, then transfer to a wire rack to cool completely. Store in an airtight container for up to a week.