Preheat oven 155°C fan.
Begin with the pistachio meringue base. Take a large piece of parchment paper, with a pencil draw around the cake tin, place the paper on a baking sheet. Whisk the egg white until stiff peaks form, add the sugar a teaspoon at a time. When the meringue is thick and glossy, fold in all but 2 tsp of the pistachios. Pour the meringue onto the parchment, with a palette knife spread it out to form a 23cm disc. Bake for 45 minutes. Cool.
Put the blackcurrants, 1 teaspoon lemon juice and 145g caster sugar into a small saucepan with 2 tablespoons water. Bring to the boil, then simmer for 5 mins or until the fruit is soft. Remove and cool a little. Press the mixture through a fine sieve into a bowl to remove the seeds and skins, (a ladle is really good for this job). Repeat with the raspberries and redcurrants. You should end up with 240g of each, so make sure you push through all the pulp. Set to one side to cool.
Cut a large freezer bag down one side. Line the cake tin. Make sure there’s plenty of overhang, to aid removing the cake from the tin. (I don’t use clingfilm because I find it tears easily). Place the meringue disc in the bottom of the tin, you may need to trim it a little.
Now for the ice cream: separate the eggs, place the 3 egg yolks and the sugar in a medium bowl with the vanilla bean paste. Whisk until pale and thick. In a separate bowl, whip the cream until it’s the consistency of thick yogurt. Fold into the egg yolks. Wash the whisk, now whip up the 2 egg whites until stiff peaks form. Fold one tablespoon into the cream mixture until fully incorporated. Then gently fold in the remainder. Pour half of the mixture into the cake tin. Now drizzle one third each of the two cooled fruit sauces here and there on the top. Add the remaining mixture, then add a little over a third of each sauce, leaving some for serving. Sprinkle with the remaining chopped pistachios. Pop it in the freezer, without covering. Once it’s been in the freezer for a couple of hours, then cover and continue to freeze 8 hours.
Remove the cake from the freezer approximately 10 minutes before serving. Place on a plate, and decorate with fresh berries. Serve with the remaining fruit sauces, I blend them.