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