To make the dulce de leche preheat the oven to 220 celsius (425 Fahrenheit) and pour the condensed milk into a casserole dish and sprinkle with sea salt and stir to combine. Covering with a tight fitting lid or foil and place the casserole dish inside a large roasting pan and fill with water so that the water level is ½ the height of the casserole dish. Bake for 90 minutes until golden. Set aside to cool completely. If your dulce de leche appears lumpy after it comes out of the oven don’t panic. Use an immersion (stick blender) to blend until smooth and glossy.
Heat a large frying pan over a medium low heat and add the butter. Once the butter has melted add the banana slices (you may have to cook the bananas in a couple of batches) and fry until softened. Remove from the heat and set aside to cool.
Take 6 small glasses and divide the dulce de leche between them. Top with the banana slices and set aside.
In a small saucepan add the flour and sugar and whisk in a small amount of milk and combine until a smooth paste forms. Add the remaining milk and whisk and place over a medium low heat. Whisk until the mixture thickens. This can take some time, you don't need to whisk all the while, but do keep an eye on the mixture and whisk now and again to prevent lumps forming.
Remove from the heat and add the chocolate. Leave the chocolate to melt for a minute before whisking into the mixture. Divide the chocolate mixture between the glasses and refrigerate until ready to serve. Serve topped with a dollop of cream and grated chocolate.
If you decide to make the chocolate pudding on it's own you may need to increase the sugar slightly to counteract the bitterness of the 70% cocoa chocolate, depending on your tastes.