Heat the milk and butter and bring to the boil.
Mix the tapioca flour with a little water to make a paste. Remove milk from the heat and add tapioca paste. Mix quickly and thoroughly to avoid lumps.
Cook for a further 5 minutes, stirring occasionally. Add 3/4 of the parmesan cheese.
Combine the cheese sauce with the macaroni and flaked hot smoked salmon
Spoon the mixture into a large baking dish or alternatively 4 individual ramekins and sprinkle with remaining parmesan cheese. Bake for 15 minutes at 180 degrees C.