Put the fish into a plan large enough to hold it comfortably and cover with milk and water.
Bring gently to the boil.
By the time it comes to the boil the fish should be just cooked – if its not then give it another minute or so.
Remove the fish from the pan and allow to cool.
Melt the butter in another pan on a medium heat.
Add the leek and pinch of salt along with the curry powder.
Cover and allow to sweat without colouring for about 10 minutes until the leeks are very soft.
Dust the plain flour into the soft leeks, stir and combine and continue to cook for 2 minutes.
Pour the haddock cooking liquor throughout a sieve onto the flour and leeks.
Add the par cooked apache potatoes and turn up the heat slightly, simmer gently for 20-25 minutes.
Add the frozen peas to the pot and break the haddock into flakes and add this to the pot too.
With sharp scissors, snip the coriander and add into the haddock / potato mix too.
Gently stir until all is evenly combined.
Carefully pour all into a suitably sized oven proof dish and allow to cool slightly.
Put the rooster potatoes into a large pan and cover with cold water.
Add 2 tsp salt and cook on a medium heat until fully tender.
Drain the roosters into a colander, discard the water and return the cooked potato to the pot.
Reduce the heat and dry out a little.
Using a potato masher, mash the potato then beat in the cold butter.
Pour in the warm milk and stir until smooth.
Add the spring onions and a pinch of chilli flakes, stir well then add the egg yolks and stir until evenly mixed.
Spoon the mashed potato on top of the ‘Cullen Skink’ and spread evenly.
Make a few ridges with the tips of a fork.
Bake in a preheated oven (190°C) for 35 minutes until heated through and crispy golden on top.