Fresh apricot tart with basil custard filling

Method
Prep:50min  ›  Cook:30min  ›  Extra time:4hr  ›  Ready in:5hr20min 

1. Preheat oven to 180 C / Gas 4.
2. Whisk plain flour, wholemeal flour, ground almonds, 1 tablespoon sugar, lemon zest and salt together in a large bowl. Rub in butter until mixture looks crumbly. Stir in buttermilk until dough comes together.
3. Press pastry evenly over the bottom and 1cm up the sides of a large 30x40cm flat tin.
4. Bake in the preheated oven until lightly browned, about 20 minutes. Place tin on a wire rack to cool completely, about 1 hour.
5. Whisk egg yolks, 125g caster sugar and cornflour together in a heavy-bottomed pot. Whisk in milk. Add whole basil sprigs.
6. Cook milk mixture over medium heat, whisking constantly, until mixture begins to steam, about 8 minutes. Reduce heat to low. Remove basil sprigs with tongs and discard. Whisk vigorously until custard thickens, about 1 minute.
7. Set a sieve over a large bowl. Pour custard into the sieve; use a spatula to press it through the sieve into the bowl. Whisk vanilla extract into the custard. Press a piece of cling film directly onto the surface. Refrigerate until cold, about 3 hours.
8. Pour cooled custard over the pastry base; spread evenly to edges of with a spatula. Arrange apricot slices on top.
9. Scoop apricot jam into a small microwave-safe bowl; microwave on high until melted, about 1 minute. Brush jam over apricot slices.