Rinse the potatoes well, chop in several places with a toothpick, rub with salt and a little vegetable oil.
Wrap each potato in foil and bake at 220 degrees for about an hour.
For the sauce, finely chop the onion, herring fillet, gherkins, garlic and dill. Mix everything, add sour cream and salt if necessary. For tenderness, you can kill everything in a homogeneous mass with a blender.
Remove the potatoes from the foil, make an incision, put the sauce in it and serve.