1. Blanch the Brussels sprouts in the chicken stock for approximately 3 minutes. Pop the tomatoes into boiling water, hold under running cold water and skin them. Slice the tomatoes and add to the chicken stock.
2. Season well with salt, pepper, oregano and the freshly grated nutmeg. Crease an oven proof dish with the butter. Preheat the oven to gas mark 6 (400° F or 200° C). Transfer the mixture into the casserole.
3. Cut the Parma ham into thin strips and spread together with the cheese over the casserole. Put in the centre of the oven and bake for approximately 20 minutes.