Krempita (Montenegrin Vanilla Custard Slice)

Instructions

1. Heat the oven to 200°C (400°F). Unroll the pastry sheets onto trays lined with parchment and trim each to a square slightly larger than a 23 cm (9 in) pan. Prick all over with a fork.
2. Cover each sheet with parchment and a second tray to keep the pastry flat. Bake for 15 minutes, then remove the top tray and parchment and bake for 8 to 10 minutes more, until deep golden and crisp. Cool, then trim to fit the pan.
3. Whisk 100 ml (scant 1/2 cup) of the cold milk with the cornstarch until smooth, then whisk in the egg yolks.
4. Heat the remaining milk with the sugar, vanilla and salt until steaming. Pour about a third over the yolk mixture while whisking, then pour everything back into the pan.
5. Cook over medium heat, whisking constantly, for 3 to 5 minutes, until the custard thickens and bubbles. Keep whisking for 1 more minute so the yolks are fully cooked. Transfer to a bowl, press plastic wrap onto the surface and chill until cold, about 1 hour 30 minutes.
6. Whip the cream to soft peaks. Beat the cold custard briefly until smooth, then fold in the cream in two additions.
7. Line the pan with parchment, leaving an overhang. Lay one pastry square in the bottom, spread over the custard in an even layer and top with the second square, pressing lightly.
8. Chill for at least 4 hours or overnight. Dust with icing sugar, lift out using the parchment and cut into squares with a serrated knife.

Tips

• Weighing the pastry down under a second tray keeps it flat, so the slices stay neat. Bake one sheet at a time if your oven is small, and trim the baked edges with a serrated knife.
• Press plastic wrap onto the custard as it cools to stop a skin forming, and beat it smooth before folding in the cream. If lumps form while cooking, pass the hot custard through a sieve.