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1
In a heavy-based saucepan melt the butter over a medium heat and fry the onions and carrot for two minutes or so, until the onion becomes translucent.
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2
Heat the oven to 220 degrees.
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3
While this is happening, get the milk very hot (don't boil it over).
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4
Stir the flour into the buttery veg, and cook gently for two minutes - it can brown a little but not burn.
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5
Pour in a little of the hot milk and stir to amalgamate, then more, until all used up.
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6
Cook over a very low heat, stirring occasionally, until you have a nice thick white sauce with no taste of flour remaining.
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7
While the sauce is cooking, boil your peeled and chunked potatoes until cooked through, then drain (reserving a little of the liquid) and mash them.
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8
You want nice moist mash, so if they feel too dry, add a little of the potato water back in.
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9
Season the mash to taste.
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10
Pour the sauce into a suitable gratin dish, or an oven-proof casserole, then add the broken up pollack and kippers plus their oil and mix to distribute the fish more-or-less evenly in the sauce.
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11
Gently spoon the mash on top of the fish and sauce so it doesn't sink in, and spread to cover.
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12
Drag the surface of the spuds with a fork to make ridges that will brown nicely in the oven.
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13
Cook in the oven for 20 - 25 minutes until the top is starting to brown.
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14
To save cleaning the oven it's a good idea to have the gratin dish in a big roasting dish, as the sauce can bubble up and spill a little in cooking.
