Grate the potatoes and place them in a bowlful of cold water to stop them from colouring.
Line a sieve with a clean tea towel or muslin and add the grated onion and potatoes then wrap them up in the tea towel, twist the top to seal and squeeze out as much water as you possibly can.
Whisk together the eggs, flour, salt and a good grinding of black pepper in a large bowl. Add the drained vegetables and give it a good stir.
Place a heavy bottomed frying pan over a medium heat and add one Tbsp each of butter and vegetable oil. Heat until bubbling but not burning. Add scoops of the potato mixture (I use a 1/4 cup measure) and use a spatula to flatten them into thin pancakes.
Cook for 4-5 minutes, until golden, then flip over and cook for a further 4-5 minutes until both sides are well browned.
Drain on a piece of kitchen roll then place on a baking sheet in a low oven to keep them crispy while you cook the rest.
Wipe out the pan and add another Tbsp each of butter and oil, cook another batch of latkes as before and repeat until you have used all of the mixture.
Serve topped with a dollop of sour cream, some smoked salmon and a sprinkling of chives.
If you are making the latkes in advance, once cool store them covered in the fridge for up to a day then reheat in a 200C/400F/gas mark 6 oven for 8-10 minutes to serve.