1Heat a skillet over high heat.
2Add the sugar, and spread evenly. Reduce the heat to low, without stirring, until the sugar melts, and turns into a light golden caramel.
3It should take 5 to 8 minutes.
4Crush the banana to a smooth puree.
5Before the caramel gets too dark, add the banana puree, and beat until well blended.
6Add the milk, and 1/2 of the yogurt, and remove from the heat.
7In a bowl, beat the egg yolks.
8Put the banana caramel back on the stove on low heat, and add the eggs, mixing gently with a wooden spoon.
9Continue to stir over low heat, until the banana cream is thick enough to cover the spoon.
10Transfer to a bowl.
11Soak the gelatin in water, or use 2 tablespoons of neutral gelatin powder.
12Add the gelatin to the banana cream, and whisk until dissolved (if you get a few strands of banana or too little liquid just put everything in the blender for a few seconds).
13Cover the surface of the cream with plastic wrap, to prevent a crust from forming, and refrigerate.
14When the cream is almost cold, stir it until smooth.
15Add the remaining yogurt and mix.
16Divide the mixture into 4 bowls, and refrigerate for 1 to 2 hours until firm.
17To serve, place a ball of ice cream on top on each bowl, and top with still warm, melted chocolate.