>>21506332 (OP)
Here's the Escoffier recipe for sauce bigarade:
For braised duck: Pass the braising liquor from cooking the duck through a strainer and remove the fat carefully; reduce it until fairly thick. Add the juice of four oranges and one lemon to each 1 litre of reduced braising liquor so as to reconstitute it to the required consistency.
For poêléed duck: Remove the duck from the pan, add a little brown veal stock to the sediment, bring to the boil, pass through a strainer and carefully remove the fat. For each 1 litre add the following: 20 g of sugar caramelized and diluted with ¼ dl of vinegar, and the juice of four oranges and 1 lemon. Lightly thicken with diluted arrowroot.
In both cases this sauce is finished with 2 tbs of very fine Julienne of orange zest and 1 tbs Julienne of lemon zest, both well blanched.
