Preheat the oven to 250 F (120 C).
In a saucepan, combine the cream and Mars bars cut into pieces and bring to a boil, stirring constantly, until the bars are melted.
Beat the egg whites, without making them rise, just enough to liquefy them.
Pour the cream in gradually and mix well.
Distribute this cream into 4 glasses or ramekins, without filling them to the top.
Cook in the oven in a water bath for 45 minutes.
The surface should be firm, the cream set, but still trembling.
Let it cool down first in the turned-off oven for 15 minutes, then at room temperature.
Refrigerate for at least 2 hours.
Finish:
In a water bath, melt the Mars bars with the 35% cream, until smooth and homogeneous, then share the preparation in the glasses.