Place cans of condensed milk in lg. saucepan and cover with water 3/4's up the cans. Bring to a boil, reduce heat to simmer, cover, and simmer for 4 hours, replacing water as necessary.(Milk inside cans will turn to toffee). Remove from pan and allow to cool.
Cut bananas in 1/2-inch slices and cover bottom of crusts.
Spread cooled toffee over bananas.
Add another layer of bananas.
Whip heavy cream until it turns into whipped cream. Add vanilla extract, sugar & coffee crystals. Stir until well blended.
Heap whipped cream mixture on top of bananas.
Sprinkle grated chocolate on top of whipped cream.