Start by filleting the fish, then squeeze some lemon juice over the fish and sprinkle them with a little salt.
Let the fish rest while you make the rest of the dish.
Slice the potatoes and chop the anchovies.
Lay out four double sheets of tin foil.
Slice the potatoes, onions, dill and egg evenly on the four sheets.
Roll the fish filets into small rolls and place on top.
Add one lump of butter in each pack, and squeeze some more lemon juice over them.
Wrap the tin foil around the individual servings and place over an open fire for about 25 minutes, or until the fish is firm and completely white.