Heat the butter in a pan and sweat the onion without colouring for about 5 minutes. Add 3/4 of the ham and all the celery and cook until the ham is lightly gold and the celery softened.
Add the potatoes and cook for 2-3 minutes. Add the herbs and stock and simmer for 10 minutes until the potatoes are tender. Meanwhile blanch the beans for 3 minutes in boiling salted water then drain and refresh in cold water. Set aside.
Liquidise the soup in a blender and return to the heat. Stir in the beans, sweetcorn and reserved ham and season, being mindful the ham is quite salty.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.