Peel the potatoes, boil them and add the cream. Cut off the tops of the tomatoes, remove the insides and salt the insides of the tomatoes.
Grate the feta cheese and mix it with the insides of the tomatoes, black pepper and mustard. Stuff the tomatoes with this mixture.
Break the eggs 1 by 1, remove the whites, put a yolk on top of each tomato.
Beat the whites to snow and mix them with the mashed potatoes. Lay the potato mixture out into an oiled oven dish, put the tomatoes and pieces of butter on top if it.
Bake in a preheated moderate oven for 15 min., sprinkle with grated cheese toward the end.