Worth making double quantity and freezing some.
4 tbs granulated sugar
2 tbs water
2 tbs wine vinegar
1/2 pt stock
1 tbs thick-cut orange marmalade
2 large oranges
1 tbs cornflour
1 tbs water
Put the sugar into a dry saucepan and heat, stirring, till the sugar has turned to caramel — you need a good deep brown, without burning. Take off the heat and add the 2 tbs water, keeping out of range of splatters. Return to the heat and stir to blend. Then add vinegar, stock, and marmalade. Add the juice of one of the oranges. Cover and simmer gently for half an hour.
Meanwhile, shred the zest of the remaining orange and reserve. Cut a slice from the top and bottom of it and then use a sharp knife to remove all of the peel and pith. Separate into segments (do all this over a bowl and add any juice to the sauce). Put the shredded peel in a pan of cold water, bring to the boil, and drain. Replace with fresh water and simmer for about 20 minutes to soften the peel.
Back to the sauce: after the half hour is up, blend the cornflour and water, add a little hot sauce, stirring, and then add this mixture to the sauce. Stir over moderate heat until thickened, add the reserved orange segments and zest, and heat through.