Peel the potatoes, cut them into pieces and boil in salted water until softened. Drain them well, mash with a fork. Add the butter, egg and flour, mix a dough that's slightly sticky (dip your hands in flour to help you).
Season with salt and black pepper. Put the torn broccoli rosettes and pea/carrot mix in a pot with a little water. Boil 3-4 min. Pour in cold water, so that they retain their color. Drain well and mix with the cooking cream.
Sprinkle with salt and black pepper. Put the potato mixture in a buttered and floured oven dish, form a border. Pour the vegetable mixture with the cream in the middle.
Tear the mozzarella into pieces and distribute it on top of the veggies. Bake in a preheated 374°F (190 °C) oven for about 35 min. Take it out, cut it into pieces once cooled and serve.