In a heatproof bowl, combine the white chocolate, dark or milk chocolate, and neutral oil. Melt them together gently over a double boiler until smooth and glossy.

Pour the melted chocolate mixture into a mold, swirling to coat evenly. Set aside to cool until it hardens into a crisp chocolate shell.

In a mixing bowl, whip together the cream, hazelnut spread, mascarpone, and vanilla bean paste until fluffy and combined.

In a saucepan, combine frozen blueberries, caster sugar, and fresh lemon juice. Cook over medium heat until the blueberries are soft and start to burst.

In a separate bowl, combine Dutch-processed cocoa, caster sugar, and hot water. Stir until smooth.

Quickly dip ladyfinger biscuits in the soaking liquid, ensuring they are coated but not soggy. Layer them in your serving dish with the blueberry compote and filling.

Once the chocolate shell is completely set, remove it from the mold and place it atop your layered cake.

Cover the cake and chill in the refrigerator for at least 2 hours.