Chop your potatoes into 1 inch chunks (no need to peel). Trim the ends off the leeks and slice them roughly. Peel your onion and chop into 1 inch chunks.
Melt the butter in a large saucepan or casserole dish over a medium heat. When it starts to bubble, add the potatoes, leeks and onion. Turn down the heat and put a lid on. Cook for 5 minutes, stirring fairly often so that the vegetables don’t stick or colour.
Pour in the stock and bring to the boil. Put the lid back on and simmer for about 15 minutes, or until the potatoes are soft.
Whizz your soup up with a blender until smooth then put back on the heat. Add the cream and bring to a simmer, then season to taste with salt and plenty of black pepper.
Serve large bowls or mugs with thick wedges of warm bread. Delicious!