Brown the sausages all over in a little oil in a frying pan – this should take around 5 or 6 minutes – and while that’s happening put a smear of butter round the base of a casserole.
Then put in a layer of potatoes, a sprinkling of onion and seasoning and repeat the layers until all the potatoes are in, finishing off with a few flecks of butter. Now remove the browned sausages from the pan, using a draining spoon, and place these on top of the potatoes. Sprinkle in the dried herbs, pour in the milk and water, cover the casserole with a piece of foil, place it in the oven and bake for about 45 mnutes.
Then remove the foil and bake for a further 15-20 minutes, or until the potatoes are tender when tested with a thin skewer.
Preheat the oven to gas mark 4, 350°F (180°C).
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