In a medium saucepan, pour part 1 of the thickened cream and add the split vanilla bean pod. Heat over medium until simmering, then remove from heat and allow to infuse for 15 minutes.

In a mixing bowl, whisk together the caster sugar and large eggs until light and fluffy, about 3 minutes. Gradually stir in the cornstarch until fully combined.

Slowly add the infused cream, whisking to temper the eggs. Return to saucepan and cook, stirring constantly until it thickens, about 5-7 minutes.

Transfer the thickened custard to a clean bowl. Cover with plastic wrap directly on the surface and refrigerate for 1-2 hours.

Beat part 2 of the thickened cream with an electric mixer until stiff peaks form, about 3-5 minutes.

Gently fold the whipped cream into the chilled custard in three additions, taking care to preserve the airy texture.

Spoon the mousse mixture into serving cups, cover with plastic wrap, and refrigerate for at least 3 hours or overnight.