Instructions

Make Dough: Whisk durum flour, bread flour, salt, and yeast together in large bowl. Using rubber spatula, fold water, orange juice, and vinegar into flour mixture, scraping up dry flour from bottom of bowl and pressing dough until cohesive and shaggy≈and all flour is incorporated.
First Rise: Cover bowl tightly with plastic wrap and let sit at room temperature for at least 8 hours or up to 18 hours.
Fold and Rest: Mix chocolate and orange zest together in bowl, breaking up large clumps of zest with your fingers. Sprinkle half of chocolate mixture evenly over dough. Using greased bowl scraper or your wet fingertips, fold dough over itself by lifting and folding edge of dough toward middle and pressing to seal. Turn bowl 90 degrees and fold dough again; repeat turning bowl and folding dough 2 more times. Sprinkle remaining chocolate mixture over dough and repeat folding dough 4 more times (for a total of 8 folds). Flip dough seam side down in bowl, cover with plastic, and let rest for 15 minutes.
Lay 18 by 12-inch sheet of parchment paper on counter and spray lightly with vegetable oil spray. Transfer dough seam side up to lightly floured counter and pat into rough 9-inch circle using your lightly floured hands. Using bowl scraper or your floured fingertips, lift and fold edge of dough toward center, pressing to seal. Repeat 5 more times (for a total of 6 folds), evenly spacing folds around circumference of dough. Press down on dough to seal, then use bench scraper to gently flip dough seam side down.
Shape Dough: Using both hands, cup side of dough furthest away from you and pull dough toward you, keeping pinky fingers and side of palm in contact with counter and applying slight pressure to dough as it drags to create tension. (If dough slides across surface of counter without rolling, remove excess flour. If dough sticks to counter or your hands, lightly sprinkle counter or hands with flour.) Rotate dough ball 90 degrees, reposition dough ball at top of counter, and repeat pulling dough until taut round ball forms, at least 4 more times. Using your floured hands or bench scraper, transfer dough seam side down to center of prepared parchment.
Second Rise: Cover dough with inverted large bowl. Let rise until dough has doubled in size and dough springs back minimally when poked gently with your finger, 1 to 2 hours.
Thirty minutes before baking, adjust oven rack to middle position, place Dutch oven with lid on rack, and heat oven to 475 degrees. Using sharp knife or single-edge razor blade, make one 6-inch-long, ½-inch-deep slash with swift, fluid motion along top of loaf. Carefully remove hot pot from oven and, using parchment as sling, gently transfer dough to hot pot. Working quickly and reinforcing score in top of loaf if needed, cover pot and return to oven.
Bake: Reduce oven temperature to 425 degrees and bake loaf in covered pot for 30 minutes. Remove lid and continue to bake until loaf is deep golden brown and registers at least 205 degrees, 10 to 15 minutes. Using parchment sling, carefully remove loaf from hot pot and transfer to wire rack; discard parchment. Let cool completely, about 3 hours, before slicing.