Place in the oven and bake for 30 minutes, until the surface is crisp but not coloured. Remove from the oven and leave to cool in the tin.
To prepare the filling, place the mascarpone, sugar and rose water in a bowl and whisk briefly to dissolve. Add the cream and beat with a hand mixer or whisk until soft peaks form; do not overbeat or it will be too stiff to spread.
Now comes the fun part: when the meringues have cooled, dust them lightly with icing sugar. Prepare a large sheet of fresh baking paper, cover the tops of the meringues with it, place them on a flat plate or board and turn them over. Carefully remove the baking paper from the bottom of the meringue.
Spread most of the cream over the meringue, leaving an edge close to you lengthwise. Spread the raspberries over the cream, then add the rose petals and pistachios.
Fold the long edge towards you to start rolling, then roll the rest into a log using the paper. Don’t worry if it cracks – it will be surprisingly pliable within reason. Shape it slightly with your hands.
Carefully transfer the log to a serving dish – cut the paper around the log to leave only the bottom piece. Chill for at least 30 minutes before serving.
Just before serving, dust the log with icing sugar, sprinkle with the remaining rose petals and pistachios and serve with the remaining raspberries on the side. Cut the slices with a sharp, non-serrated knife.
