Dip the biscuits briefly in the milk, then arrange them in a rectangular oven dish. Mix the sour cream and chocolate spread well until homogeneous.
Take 1/3 of the mixture and smear the biscuits with it. Then cut the bananas into round slices. Next place 2 layers of biscuits and cream but leave a little extra cream for the final layer.
Decorate with walnuts on top. Leave the cake for 4-5 hours in the fridge to harden.