Sweat the spring onions in the butter until they soften. Add the potatoes and coat with the butter, stirring to prevent sticking. Cook for 5 minutes.
Now add the flour, stirring and cook for a minute or so, then add the stock and half the mint. Bring to the boil then reduce heat and simmer for about 10 minutes until the potatoes are cooked but not collapsed.
Season and sprinkle with the remaining chopped mint to serve.