1Chop sponge into thirds, split each section thru into thinner slices (halves or thirds).
Into large bowl cover bottom n sides with sponge.
Peel n slice banana.
Drain boysenberries, seperate juice mix in milk to juice, Use a lil to pour over sponge in places, layer in boysenberries, sliced banana, whipped cream, then sponge, pour in a little more juice n milk, repeat all layers, should be near top of dish, top with all of custard.
Ideally leave to settle a little prior to serving.