Line a heavy large baking sheet with parchment paper. Mix the flour, cocoa powder, sugar, orange peel, and salt in a food processor
. Add the butter. Blend
until clumps form. Add 2 tablespoons of ice water and blend. Add more ice water, 1 tablespoon at a time, until the dough forms. Turn the dough
out onto a work surface and knead
briefly to form a smooth dough. Gather the dough into a ball then divide the dough into 8 equal pieces. Flatten each piece into a disk.
Press 1 dough piece on the prepared baking sheet into a 4 1/2-inch round. Spoon 1 generous tablespoon of the marmalade into the center of the round. Fold the dough border in to form a 3-inch round and allow the center of the crostata to remain uncovered. Pleat loosely and pinch the dough to seal any cracks. Repeat with the remaining dough pieces and marmalade, spacing the crostatas evenly apart. Cover and refrigerate the crostatas until they are cold, at least 45 minutes and up to 4 hours.
Preheat the oven to 375 degrees F.
Bake the crostatas until the crusts are set, about 18 minutes. Cool for 10 minutes. Slide a metal spatula
under the crusts to free the crostatas from the baking sheet. Garnish
with the candied orange peel and serve warm.