Heat the butter in a large shallow pan until the butter is foaming, then add the spring onions and cook for a few minutes.
Meanwhile, cook the broad beans in a pan of boiling water for 2-3 minutes, or until they are tender enough to slip the skins off, if you so wish.
Place the halved Baby Gem lettuces cut-side down on top of the spring onions and add the vegetable stock to the lettuce, enough to nearly cover. Scatter over the drained broad beans (I prefer mine skinned - they are just a little brighter and softer that way but skin on is fine also). Add the peas, season lightly with salt and freshly ground black pepper and simmer for a few minutes.
Finish with some mint leaves and serve once the vegetables are tender. This dish is lovely on its own but it is equally delicious paired with some old-fashioned English ham.