Firstly assemble the dish. Scatter the haddock, leek and parsley over the bottom of a shallow microwavable dish and mix together with your fingers or a spoon. Drizzle over half the cream and 5 tablespoons of water. Lay the potato slices over the fish and leeks and drizzle over the remaining cream. Season the potatoes with a little salt and plenty of black pepper.
Put the grill on high. Cover the dish with cling film and pierce it a few times. Microwave the pie on the highest setting for 8-10 minutes until everything’s bubbling away and the potatoes are tender when poked with a knife. Whip off the cling film and put the dish under the grill until the potatoes are golden. Leave to rest for a minute, then serve straight from the dish.