Peel the potatoes, bring a pan of water to the boil, then boil for about 5 minutes (and no longer than 8). Drain and rinse with cold water, then let totally cool in the fridge.
When cool, grate the potato into a large bowl, then fry the onion and bacon together in a little olive oil for about 8 to 10 minutes or until the onion is softened and the bacon cooked and a little crisp/browned. Then add the butter to the pan so that it melts before adding the bacon and onions to the potato bowl.
Add the cheddar, about two thirds of the chives and a bit of salt and plenty of pepper to the bowl and mix thoroughly with a wooden spoon or even with your hands.
Now heat up a little oil in a frying pan, then tip the potato mixture into the pan. Flatten and shape it a little, then leave to cook for about 8 minutes or until the bottom is nicely crisped up. Then put a plate over the top of the pan and flip the pan over so that the rosti falls out onto the plate. Then carefully slide it back into the pan so that the other side can cook.
Leave to cook for about another 8 minutes, then take off the heat, sprinkle with the rest of the chives and cut into slices. Serve immediately (with poached eggs if you like!)