Open-freezing means you freeze a dish just until it is firm, without wrapping it. Then, when you do wrap it, it won't get squashed.
Heat oven to 140C/fan 120C/gas 1. Line a 33cm
x 23cm Swiss roll tin with baking parchment. For the
meringue, mix together the cornflour, coffee and
vinegar, and set aside. Whisk the egg whites to stiff
peaks, then gradually beat in the sugar, a spoonful
at a time, until quite thick. Whisk in the coffee mix.
Spoon the meringue onto the paper and gently
spread, giving the top a few swirls. Scatter over the
pistachios. Bake for 35-40 mins until it feels crisp.
Meanwhile, make the filling. Slice the mango either
side of the stone, peel, then finely chop the flesh. Beat
the mascarpone, then stir in the mango. Whip the
cream until thick and fold into the mango mix. Halve
the passion fruit, scoop out the inside and set aside.
When the meringue is cooked, leave in the tin for
10 mins, then lift out and put on a cooling rack,
paper-side down. Dust a sheet of baking parchment
with icing sugar and, when the meringue is cold, tip
it on, paper side up. Peel off the lining paper and
spread the cream over. Drizzle over the passion fruit
and roll up using the paper as a guide. Open-freeze (see 'Try' below) on a board, wrap in foil and freeze for up to 1 month.
To serve, unwrap and thaw in the fridge for about 1 hr. Sift with icing sugar and serve in slices.