Peel apples, remove stalk and core and cut into pieces.
In the meantime crush crispbread slices thoroughly and mix the cold butter, sugar and cinnamon.
Crumble about one third of the mass into the 6 preserving jars.
Spread apple pieces onto crumbles and sprinkle with rum.
Spread the remaining crispbread mass into glasses.
Bake at 180°C for about 25-30 minutes in the middle of a pre-heated oven.
Serves well with custard.