Preheat the oven to 175°C and line a 23 × 33cm tin with parchment. Begin with the crust—bring together the flour and sugar, then work in the cold butter until the mixture resembles soft, coarse crumbs. Press into the tin and bake for 15–20 minutes, until lightly golden. Allow to cool completely.
For the custard, gently heat the milk until just simmering. In a separate bowl, whisk the sugar, cornflour, and egg yolks until smooth, then slowly temper with the warm milk before returning everything to the pan. Cook over a steady heat, stirring continuously, until thickened and glossy. Remove from the heat, stir through the vanilla and salt, then cover the surface and leave to cool.
Once the custard has fully cooled, fold through the softly whipped cream to create a light, airy finish. Spread evenly over the prepared crust and refrigerate for at least 4 hours, until delicately set.
To serve, lift from the tin, slice into neat squares, and finish with a light dusting of icing sugar and a few fresh mint leaves, if you like.
