In a saucepan, heat the heavy whipping cream with the scraped seeds and pod of a fresh vanilla bean over medium heat until it simmers, about 5 minutes.

Remove from heat, cover, and let the mixture infuse for 10 to 15 minutes.

While the cream is infusing, whisk together the eggs and caster sugar until fluffy and pale.

Gradually mix in cornstarch to create a smooth base.

Slowly pour the warm cream into the egg mixture, whisking continuously to prevent curdling for about 1 to 2 minutes.

Return the mixture to the saucepan and cook over low heat, stirring constantly for about 5 minutes until thickened.

Transfer the custard to a bowl, cover with plastic wrap touching the surface, and refrigerate for 1 to 2 hours.

Whip the second part of the heavy whipping cream on medium speed until stiff peaks form, about 3 to 5 minutes.

Gently fold the chilled custard into the whipped cream in 3 to 4 additions.

Pour the mousse into serving cups and refrigerate for at least 3 hours, or overnight.

Serve topped with fresh berries or chocolate shavings.