Preheat the oven to 230°C/450°F/gas 8.
Put the potatoes into salted boiling water and bring back to the boil for 2 minutes.
Carefully add the eggs to the pan and cook for a further 8 minutes until hard boiled, by which time the potatoes should also be cooked.
At the same time steam the spinach in a colander above the pan. This will only take a minute. When the spinach is done, remove from the colander and gently squeeze any excess moisture away.
Then drain the potatoes in the colander.
Remove the eggs, cool under cold water, then peel and quarter them. Place to one side.
In a separate pan slowly fry the onion and carrot in a little olive oil for about 5 minutes, than add the double cream and bring just to the boil. Remove from the heat and add the cheese, lemon juice, mustard and parsley.
Put the spinach, fish and eggs into an appropriately sized earthenware dish and mix together, pouring over the creamy vegetable sauce.
The cooked potatoes should be drained and mashed - add a bit of olive oil, salt, pepper and a touch of nutmeg if you like. Spread on top of the fish. Don't bother piping it to make it look pretty - it's a homely hearty thing.
Place in the oven for about 25-30 minutes until the potatoes are golden.