From 1922:
Take 1 packet red jelly and dissolve as usual, and place to cool until almost firm. Make 1 pint of plain boiled custard and stand aside to cool. When nearly cool, place jelly in a bowl and slowly pour in custard, and stir until well mixed, then leave in a cool place until firm. This is an excellent, cool and easily made summer pudding, and will tempt delicate children and invalids.