I make this using the exact same blend of flours that i use in my plain loaf so usually it is about 30% rye 70% strong white but any blend will be fine.
When you make up your dough for a plain loaf, aim to make an extra 500g or so.
Take 500g of your dough and add to this 1 egg, two chopped over-ripe bananas, 50g sultanas, 50g currents, 50g sugar. salt as you would your usual loaf. mix together and allow to prove in a bowl or a jug. due to the sugar it will rise well. When risen form it into a ball, it makes a very sticky dough so be prepared and use plenty of flour when you do this. transfer into a greased tin and leave to rise for a second time.