Boil the potatoes for 15 minutes, peel and slice. Dice the onion, cut the leek into rings and finely pluck the chard. Mix the sour cream with the crème fraîche and pepper.
Butter a baking dish and layer in a layer of potatoes. Scatter diced onions and leek over the top and cut chives and dill over them with the scissors. Spread the matjes cut into pieces on top and pour some of the sauce over them. The second layer is exactly the same, but also with Swiss chard. Spread the rest of the sauce over the last layer, sprinkle the toasted bread cubes over it and press in lightly.
Bake at approx. 200 ° on the lowest rack of the oven for 40 minutes.