Melt the butter in a large saucepan over a medium heat.
Add the onion and leeks and cook for 5-7 minutes, stirring often until softened.
Add the garlic, salt, celery salt, and pepper and cook for a further minute.
Add the potatoes and stock. Stir, bring to the boil and simmer for 20 minutes – until the potatoes are starting to fall apart. Turn off the heat.
Using a slotted spoon, remove 2 scoopfuls of the potato and leek mixture and place in a bowl – this is for topping the soup later. (This is optional)
Blitz the remaining soup either carefully using a stick blender, or by transferring it to a blender that can be used for hot liquids.
Pour the soup back into the pan along with the cream and heat through on a medium heat for 2-3 minutes until hot.
Spoon into bowls and top each bowl with a spoonful of the potato/leek mixture.
Swirl over a drizzle of cream and top with chopped chives and a pinch of black pepper.
