Making the Vanilla Custard:

Separate the eggs, placing the yolks in a small bowl. Set aside the whites or discard.
Whisk the egg yolks, sugar, and cornstarch together until smooth. Add a bit of milk if too thick.
Split the vanilla bean and scrape out the seeds. Add both seeds and pod to a pot, pour the milk over, and heat until steaming.
Gradually whisk some hot milk into the yolks, then return all to the pot. Cook on medium low until thick.
Strain through a fine mesh sieve, cover with plastic wrap, and chill for 2-4 hours.
Making the Stabilized Whipped Cream:

Sprinkle gelatin over cold water and let sit 5-10 minutes.
Whip the cream to soft peaks.
Melt the gelatin slightly, then while whipping, drizzle into the cream until stiff peaks form.
Mixing the Mousse:

Fold about ¼ of the whipped cream into the chilled custard.
Gently fold this mixture into the rest of the whipped cream.
Scoop into cups and refrigerate until set, at least 2 hours.