Cook over a medium heat until a crust forms on one side, then carefully turn each over and cook on the other side again until a crust forms. Don’t overbrown them or they will burn on the outside before they are cooked inside. After the crust forms, reduce the heat right down and cook for four to five minutes on each side, or until the vegetables are cooked through. (You’ll know from the taste whether they are cooked right through. The potato becomes sweet.)