Peel and roughly chop the onion and potatoes.
Roughly slice the white part of the leeks, then cut the green stems into small pieces and set aside.
Melt the butter in a large saucepan then gently fry the leek whites and onion over a medium heat for 4-5 minutes until they start to soften.
Add the chopped garlic, stir for another minute or so then tip in the potatoes.
Pour over the stock and simmer for 20 minutes or so until the potatoes are soft.
While everything is bubbling away, crack on with the topping; fry the bacon in a splash of oil until crispy then remove from the pan and snip into little pieces with scissors.
Add the chopped green leek to the bacon fat and fry gently for 4-5 minutes until soft.
Blitz the vegetables and stock until smooth and creamy, then ladle into bowls. Add a swirl of your favourite salad oil, creme fraiche or double cream, then top with the leeks and bacon.