For me, the combination of chocolate and citrus during the holidays is a given. I packed that combo into these decadent biscotti that are perfect for dipping in an afternoon coffee or evening vin santo.
Preheat the oven to 350 degrees F. Line a rimmed baking sheet with parchment paper, dust with 1/4 cup flour and set aside.
In a medium bowl, combine the sugar, butter, orange marmalade, orange zest and salt. Using a handheld mixer, beat on medium speed until the mixture is smooth, light and fluffy, about 2 minutes. Beat in the eggs one at a time. Add the remaining 2 cups of flour, cocoa powder and baking powder and beat until just blended. Using a rubber spatula, stir in the chocolate chips.
On the prepared pan, form the dough into a 3-by-13-inch log. (Using a small offset spatula or dusting your hands with flour will help keep the dough from sticking to your hands.) Bake until the log is firm to the touch, cracked on top and looks dry, about 35 minutes. Cool for 30 minutes on the tray.
Place the log on a cutting board and using a serrated knife, cut the log on a diagonal into 1/2-inch slices. Arrange the biscotti cut-side down on the tray. Bake until they are a dry and fragrant, an additional 20 to 25 minutes. Transfer the biscotti to a cooling rack and cool completely.