Cut the bread into slices 1 cm thick. the crusts can be cut. (I don't do this) bread is better to use black or gray. You can also test, but in this case it is undesirable to store the cake for a long time, since the bread will get wet. And you can prepare a snack from black bread in advance, 10-12 hours before serving.
The size and shape of the cake is according to your taste and desire. I'm baking two small cakes. 15*5*5 see