In a food processor, beat the graham crackers or digestive cookies until finely ground.
Melt the butter in a deep pan over medium to low heat.
When it has melted, add the ground cookies. Mix with a spatula to combine.
When the mixture starts to resemble wet sand, remove from heat. Add 50 g of chocolate. Continue mixing away from heat until the chocolate melts and is distributed evenly in the mixture.
Press mixture onto the bottom and sides of a round 26 cm spring form pan or a 10x35 cm rectangular baking pan. Use the bottom of the glass to press the mixture firmly onto the bottom and the sides of the pan.
Refrigerate the pan so that the mixture can chill, for 15-20 minutes.
Clean the deep pan and place over low heat. Add the condensed milk (dulce de leche) that should by now have a lovely caramel taste and color. Heat until it warms up and melts and add 1 pinch of salt.
Add the 100 g of chocolate. Remove from heat and continue to stir until the mixture is completely combined.
Remove the baking pan from the refrigerator. Add the caramel mixture over the pie base and refrigerate again for 2-3 hours, until it completely chills.
Before serving, prepare the bananas. Slice them and toss them in the lemon juice so that they don’t turn brown.
Beat the heavy cream with the caster sugar and vanilla extract, until it becomes like thick yogurt.
Decorate the pie with the sliced bananas and top with whipped cream.