Take the jar and turn it upside down. Press into the cake. This will cut perfect circles for you.
The leftover cake that is not in circles can be crumbled up and sprinkled into the jars. No cake left behind.
Place a layer of cake at the bottom of the jar. Pour in some freshly churned frozen custard on top of the cake. Repeat this, 1 more cake layer topped with ice cream. You can sprinkle some cake on top if there is space in your jar. Place the lid on your jar and place in the freezer.
Repeat this until all your jars are filled and your cake and custard is used.
Place the jars into the freezer and allow them to set for a couple of hours.