Grate the potatoes and onion on a coarse box grater. Wrap in a clean tea towel and squeeze out as much liquid as possible. Transfer to a large bowl and mix in the flour and plenty seasoning. Stir in the egg.

Heat a little of the oil in a large non stick frying pan. Use 2-3 tbsp of the mix per fritter and drop into the pan, cooking for 3-4 mins on each side over a medium-high heat, using a spatula to turn. Transfer to a plate lined with kitchen paper and continue with the remaining oil and mixture (it's best to cook in batches so as not to overcrowd the pan).

Serve 3 fritters per person, each stack topped with the soured cream, avocado and a fried egg. Sprinkle over spring onions to serve.