Heat the oven to 200°C (392F).
Put the potatoes in a large pot with water and salt.
Bring to a boil and leave to cook, with the lid on, for 30-35 minutes, or until they become soft and pass the fork test.
Drain the potatoes from the water.
Oil the tray lined with baking paper. Arrange the potatoes and smash them with the flat bottom of a glass or a potato masher, enough to flatten them.
Leave the smashed potatoes on the tray for another 5 minutes so that the excess moisture evaporates.
Brush each potato with melted butter, sprinkle with salt and pepper.
Bake them for about 30 minutes, or until they become golden and slightly crispy.
Sprinkle the baked potatoes with green onions and fresh dill.