Cut the potatoes in half lengthwise. Dig out the insides deeply and arrange them in an oven dish smeared with butter.
Begin stuffing the potatoes: first with a layer of the mayonnaise mixture, then with the 2nd mixture with fillet.
Put the potatoes in a preheated 392°F (200 °C) oven and bake 50-60 min.
Finally, sprinkle the potatoes with the grated cheese and bake for a few more min. in the oven until it melts and crisps. Your dish is now ready!