Blitz the pomegranate seeds in a blender, then strain through a fine sieve. You should end up with approx 150g juice. Pour the juice into a saucepan with the zest & juice of half a lime and the sugar. Bring to the boil and simmer for 2-3 minutes. Mix the cornflour with the water. Reduce the heat, then add the cornflour, stir, bring back to the boil, then simmer until the syrup thickens. Cool, add a few prepared pomegranate seeds. Set to one side.
Line a 900g loaf tin with baking parchment. In a large bowl, whisk the egg whites with an electric hand whisk until stiff, set aside. In another bowl, whisk the yolks with the icing sugar until pale and starting to thicken. Finally, in a third bowl, whip the cream until it’s the consistency of yogurt, add the lime zest. Fold the yolk mixture into the whipped cream until combined, then fold in the egg whites and the broken meringues.
Spoon half of the cream mixture into the tin and freeze for 30 minutes or until just set (keeping the rest of the cream mixture in the fridge). Once set, take the tin out of the freezer and drizzle over some of the pomegranate syrup. Reserve the rest to decorating later. Top with the remaining cream mixture & return to the freezer for another 30 mins. Now add the pistachios and gently fold them in. Cover and freezer for at least 2 hours before serving.
Turn out onto a serving plate and peel away the parchment paper. Decorate with the remaining pomegranate seeds and syrup. Store in the freezer for up to one month.