Beat the mascarpone, sugar and vanilla until smooth. In a separate bowl, whisk double cream until it is softly whipped. Fold mascarpone mix into the whipped cream, then set aside.
Cut 8 passion fruits in half, scoop pulp into a small bowl and stir in the orange juice. Slice the crusts off the brioche and cut each slice into quarters.
Lay the brioche (or cake) in the bottom of a trifle dish or glass bowl. Top this with a half of the passion fruit pulp and half of the peach slices, then spoon over half of the mascarpone cream. Repeat the layers once more (keeping a few peach slices back), topping off with a layer of mascarpone. Use the pulp from the last passion fruit and the reserved peach slices to decorate. The trifle will keep in the fridge for up to a day (decorate just before serving).