In a large pot, melt the butter over a medium heat.
Add the potatoes and leeks and saute for 2-3 minutes.
Add the flour and nutmeg and stir in to incorporate well.
Pour in the stock and bring to a simmer then cover and reduce heat to low, cook for 30 minutes.
Remove from heat and stir in heavy cream and season with salt and pepper. Puree the soup with an immersion blender.
Serve hot or cold topped with chopped chives or parsley.