Roast duck

1. Preheat oven to 190C.
2. Stir together salt, coriander, cumin, and pepper.
3. Pat duck dry and sprinkle inside and out with spice mixture.
4. Cut 1 half of orange into quarters and put in duck cavity with thyme, marjoram, parsley, and 4 onion wedges.
5. Place into the oven and roast for 100 minutes.
6. Tilt duck to drain juices from cavity into pan and transfer duck to a cutting board, reserving juices in pan.
7. Let duck stand 15 minutes.
8. Strain the cooking juices removing the top layer of fat and set aside.

Sauce

1. Heat sugar in a dry, heavy saucepan over moderate heat, until it begins to melt.
2. Add orange juice, vinegar, and salt (use caution; mixture will bubble and steam vigorously) and simmer over low heat.
3. Stirring occasionally, until caramel is dissolved.
4. Remove syrup from heat and add in the reserved cooking juices about 1 cup.
5. Stir together butter and flour to form a roux.
6. Bring pan juices to a simmer in a heavy saucepan, then add roux, whisking constantly to prevent lumps.
7. Add orange syrup and zest and simmer, whisking occasionally, until sauce is thickened slightly and zest is tender, about 5 minutes.