Finely chop onion, celery and carrot
In a heavy bottomed pan, sauté the onion, celery and carrot in the butter and oil until soft
Add the peas, stock, bay leaves and thyme
Bring to the boil
Season with salt and pepper
Simmer for at least an hour, until the peas turn to puree
Chop or pull the ham, and add most to the soup
Warm through, then serve into bowls, adding the remaining ham and parsley to garnish