Bring the port wine to the boil together with the blood orange juice, add the orange peel and let it steep for about 15 minutes over a very low heat. Take off the stove and remove the orange peel. Stir in the currant jelly and the cornstarch dissolved in a little cold water and add the cranberries. Bring to the boil again briefly until the cornstarch binds.
Remove from heat, let cool down a bit, stir in the ginger and season with mustard and salt. Serve cold.