Lightly toast the roll under a moderate heat and cool slightly.
Spread the mayonnaise onto both halves of the roll.
Place the pigs in blankets on top of one half of the roll.
Place the onion slices on top of the pigs in blanket.
Loosen the cranberry sauce with the lemon juice and spoon this over the pigs in blankets.
Put the other half slice of roll on top.
Courtesy of Phil Vickery for Kingsmill