Place a pot with the milk over a medium-high heat. Scrape the vanilla bean's seeds out, then add them to the milk with the vanilla pod. Heat the milk to a scorching temperature without letting it boil.

2 tablespoons of the granulated sugar should be taken out and put aside.

Whisk the egg yolks, corn starch, and remaining sugar together while the milk is heating. Return the mixture to the heat after whisking in the heated milk and egg yolks. Stirring continuously, cook the custard over low heat until the mixture just starts to boil and thickens. After taking it off the heat, pour it into a fresh bowl. To manufacture vanilla sugar, either discard the vanilla bean or rinse it and place it in a bin of sugar.

Before continuing with the recipe, chill the custard in the refrigerator for at least 2 hours (it must be totally cold). Place the custard bowl over a bowl of ice water to hasten chilling, and stir until cooled.

Whip the cream to a soft peak before incorporating it into the custard foundation. While you prepare the other ingredients, put the bowl back in the refrigerator.

Put the rum (or cool water) in a bowl that can be used in a microwave. Over the rum, sprinkle the gelatin in an even layer, and then wait for it to bloom.

In a heat-resistant mixing dish, combine the egg whites and the 2 tablespoons of sugar that were set aside. Without letting the bowl's bottom touch the water, place it over a pan of almost simmering water and heat it to 160°F while swirling continuously. The whites should be taken off the fire and whipped until they are fully cooled and at their peak.

In 10 second intervals, microwave the bloomed gelatin until it is warm to the touch. Add a half cup of the mousse, rapidly, to the warmed gelatin. Combine by whisking. Reintroduce the gelatin mixture to the mousse. As soon as you start, whisk until the gelatin is evenly integrated and the mousse is smooth. The whites should be quickly folded into the mousse.

While the mousse is still soft, pipe or spoon it into serving glasses. Keep chilled until set.

Serve with fruit sauce, chocolate shavings, or fresh berries.