Παραδεισένιο κέικ με φιστίκι

• Preheat oven to 160° C, fan. Cover the base and sides of a shallow 33 x 39 cm baking tray (approximately) with greaseproof paper.
• In a food processor fitted with a metal blade, put the pistachios, flour, baking powder and mastic tears (if using). Pulse until finely ground.
• In a clean bowl of a stand mixer put the egg whites and beat until frothy. Add the sugar gradually (in about 4 batches) and beat until you have a stiff meringue. Beat in the vanilla extract.
• Lower the speed to low and beat in the pistachios in two batches. Don’t over beat, you don’t want the mixture to deflate too much. You can also do this with a spatula.
• Transfer pistachio mixture on the baking tray. Spread it with a spatula. Bake for 18-20 minutes until just set. Test it with a toothpick. If it comes out dry in the centre, its done. Don’t let it dry out. 20 minutes max should be enough.
• Let the pistachio layer cool completely in the pan. You can prepare this the day before. Once cool, keep covered until ready to assemble.

Prepare the pastry cream

• Heat milk in a saucepan with about half the sugar. In another bowl whisk egg yolks with remaining sugar, corn flour and vanilla extract.
• Add half of the hot milk in the yolk mixture and whisk to combine. Add remaining hot milk in the yolks and stir again to mix.
• Strain mixture back to the pot and place over medium heat stirring constantly. Keep stirring until cream comes to a boil and thickens.
• Whisk vigorously for another minute, then take off the heat and transfer cream to a heatproof bowl.
• Immediately cover with plastic wrap, making sure the wrap touches the surface of the cream. This will prevent a skin from forming. Let cream cool to room temperature then transfer in the fridge for at least 3 hours to become cold and thick. You can prepare the cream to this stage, up to 3 days in advance.
• To finish the cream, whisk the whipping cream with the icing sugar until soft peaks form. Whisk the cold pastry cream to loosen it.
• Fold the whipping cream into the pastry cream until combined and smooth. Refrigerate until needed.
• Make the frosting by beating cream, icing sugar and vanilla together until you have soft peaks. Refrigerate until needed.

Assemble the dessert

• Using the paper for ease, remove the pistachio base out of the baking tray and onto a chopping area.
• Using a sharp knife divide the pistachio base into 3 equal sized rectangles (33cm x 13cm approximately). Place one rectangle on a serving platter. Spread with half the pastry cream. Cover with another rectangle and spread with the remaining pastry cream. Top with the last rectangle. Cover loosely with plastic wrap and place in the fridge for an hour. This will help stabilize the creamy filling and it will be easier for you to spread the frosting.
• After one hour, cover the cake with the frosting and sprinkle with the coarsely chopped pistachios. Refrigerate the cake for 2-24 hours before serving. Slice and serve.