Set the oven to 350 degrees Fahrenheit. Using parchment paper, cover a rimmed baking sheet, sprinkle with 1/4 cup flour, and put aside.
Combine the sugar, butter, orange marmalade, orange zest, and salt in a medium bowl. Beat the mixture with a hand mixer on medium speed for two minutes, or until it is smooth, light, and fluffy. One at a time, beat in the eggs. Beat in the remaining 2 cups of flour, baking powder, and cocoa until barely combined. Then, add the chocolate chips and mix with a rubber spatula.
Make a 3-by-13-inch log out of the dough and place it on the prepared pan. The dough won't stick to your hands as long as you use a little offset spatula or flour your hands. About 35 minutes into baking, the log should feel solid to the touch, be cracked on top, and seem dry. Cool on the tray for 30 minutes.
Slice the log into 1/2-inch pieces by placing it on a cutting board and using a serrated knife to cut the wood on a diagonal. Place the biscotti on the tray with the sliced side up. They should bake for a further 20 to 25 minutes, or until they are dry and aromatic. Place the biscotti on a cooling rack to finish cooling.