1. Blend flour, sugar, milk, eggs and butter in a food processor until combined. Pour into a jug and rest for 30 minutes.
2. Heat a 20cm diameter crêpe pan over medium heat. Brush with extra butter to coat. Pour 2-3 tablespoons of crêpe batter into the pan and swirl round to cover the base of the pan. Cook for 1-2 minutes or until lightly browned, turn over and cook until base is golden. Repeat with remaining batter.
3. For cheesecake custard, warm milk and the vanilla seeds in a saucepan. Whisk yolks and sugar in a bowl until thick. Whisk in flour, then milk mixture. Return to pan and cook, whisking, over low heat for 5 minutes or until mixture thickens. Cover surface with plastic wrap and refrigerate until cold. Once cold, beat in cream cheese with an electric mixer, a cube at a time, until smooth. Set aside.
4. Combine strawberries, sumac and sugar and marinate for 10 minutes.
5. For Toffeed Pistachios, place the nuts on a baking paper lined tray. Spread the sugar over the base of a large heavy based frying pan and cook over medium heat, swirling and tilting the pan as required, until the sugar has melted and turned a golden caramel colour. Pour over pistachio nuts and stand until toffee has cooled and hardened.
6. To assemble spread each crêpe (except for one, reserve for top) evenly with cream cheese custard. Spread half of the custard-spread crêpes with a layer of strawberries. Alternate layers of custard crêpe and strawberry custard crêpe onto a serving plate, finishing with the reserved top crêpe. Decorate cake with Toffeed Pistachios and extra strawberries. Serve at room temperature.
Cooked crêpes will keep for up to 2 days wrapped tightly in cling film.