Wash the potatoes and wrap in aluminum foil. Bake in a preheated oven (225 degrees) for about 1 hour.
Chop the onions. Halve the mushrooms, quarter and core the tomatoes and dice the pulp. Cut the chives into small rolls. Heat the oil. Sauté the onions in it. Add the mushrooms and fry them. Dust with flour. Pour in the broth and cream while stirring. Bring to the boil briefly. Season to taste with salt and pepper. Fold in the diced tomatoes and chives. Remove the potatoes from the foil, cut crosswise. Arrange on plates with the mushroom cream.