Make the macerated strawberries: Transfer the strawberries and the sugar to a bowl, mix well and set aside.
Make the white chocolate cream: Transfer the white chocolate to a heatproof bowl. Transfer the heavy cream, the mahleb and the mastic (if using) to a small bowl and heat until steamy. Strain it over the chopped white chocolate and stir until the chocolate is melted (if you don't use mahleb and mastic you don't have to strain it). Set aside to cool completely.
Transfer the very cold heavy cream and the vanilla extract to a bowl and beat with your electric mixer until soft peaks form. Don't over-beat. Add one third of the whipped cream to the white chocolate mixture and fold with a spatula. Then transfer the chocolate mixture back to the bowl with the remaining whipped cream and fold until everything is well-mixed.
Build the trifle: Transfer the milk and the brandy to a shallow dish. Briefly dip half of the savoiardi biscuits into the milk, break them into smaller pieces and transfer them to the glasses. Divide half of the white chocolate cream between the glasses and then add half of the macerated strawberries and half of the berries.
Reserve 1 cup cream and some berries if you want to pipe rosettes on top of the trifles. Continue with the rest of the biscuits, the cream and the fruit. Fill a piping bag with the reserved cream and pipe rosettes on top of the trifles. Decorate with the rest of the berries and some orange slices.
Double the recipe if you want to serve this trifle in a large trifle bowl.
If you use cake instead of savoiardi biscuits, transfer it to the glasses first and then brush it with some of the milk/cognac mixture.
Mastic has a strong flavor so you don't need to use much.
How to grind mastic: mix it with a teaspoon of sugar and a pinch of salt and grind it with a mortar. Mastic can leave some residue on your pot and sieve. Clean them with some warm oil and/or alcohol.
My favorite piping star tip is this
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