Heavily butter one side of each bread crust. 

Mash bananas with a fork in a bowl. 

Stack all bread crusts except for 4 pieces butter side down in a glass casserole dish. The bread should stack 3 layers deep. If it doesn't, use a smaller sized dish.

Beat the eggs in a bowl. Add the milk and sucanat and mix well.

Pour egg/milk mixture over the stacked bread in the casserole dish until just covered with liquid. 

Place mashed bananas and raisins or blueberries on the top of the soaked bread and gently fork the fruit through until evenly distributed.

Place the 4 reserved bread crusts on top of the soaked bread and fruit - butter side up. Sprinkle the butter side up bread crusts with a small amount of additional sucanat.

Bake bread and butter pudding in the oven preheated to 350 °F/177 °C for 90 minutes and until brown and crispy on top.

Grate the rind of one lemon very finely. 

Juice the grated lemon plus the other lemon and set aside. Saute the grated lemon rind in butter for 3 minutes.  

Add sugar with a very small amount of water to the rind mixture until it dissolves while still sauteing the rind. In a cup, mix the water and arrowroot and mix well ensuring there are no lumps.  

Pour water/arrowroot mixture into the pan with the rind/sugar and keep stirring until it begins to simmer and slightly thickens. Add the juice of 1-2 lemons, stir and remove from heat.

Serve sauce immediately drizzled on bowls of the cooked bread and butter pudding.