Preheat the oven to 180ºC / 350ºF / Gas mark 4.
Peel the mushrooms, carefully twist out the stalks and chop these finely. Heat the oil in a frying pan and fry the spring onions and mushroom stalks for 5 minutes. Remove from the heat and transfer to a bowl.
Stir in the ham, cream cheese, garlic purée, herbs and breadcrumbs until evenly mixed. Stir in the eggs and season with black pepper.
Spoon the mixture into the mushroom cups pressing it down with the back of the spoon and place them in a baking dish. Pour the stock around the base of the mushrooms, cover the dish with foil and bake in the oven for 30 minutes, removing the foil for the last 10 minutes.