In a saucepan, add this to the milk and add all of the above spices, onion and garlic, heat gently and allow to infuse at a very low heat for 30 mins. Strain the liquor through a hair sieve, discard the residue.
Poach the rest of the fresh and defrosted fish in this, when cooked, remove from the liquor with a slotted spoon into an oven-proof flat terrine. Break the smoked fish into bite sized pieces and scatter with the cooked prawns
Pour the resulting sauce over the fish in the terrine, cover with cling film and put into the fridge overnight.
Next day make your potato topping.
Add the cheese, reserving 10g for the top, adjust the seasoning (you may not require salt, depending on the cheese).