Make the herb oil in advance (a minimum of 24–48 hours will give you a stronger taste). Heat all of the ingredients together and then leave to infuse. Strain before using.
To make the saffron vinegar, heat all of the ingredients together. Leave to stand for 15–20 minutes. Re-heat and then strain through a sieve.
To make the terrine, first line the terrine mould with cling film.<