Par boil the potatoes with the carrot, parsnips or swede for 10 minutes, then drain them and leave to cool.
Coarsely grate the par-cooked vegetables into a large bowl and stir in the grated courgettes, spring onions and egg, seasoning.
Lightly oil a frying pan and cook the rosti mixture in small flat fritters or rostis and cook until crisp and golden on both sides. Flatten with a fish slice as they cook. They will need to be about 3-4 minutes on each side.
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