To make the pastry, place butter, sugar, vanilla and ﬂour in a food processor and whiz until ﬁne breadcrumbs form. Add egg yolk and 1 tbsp iced water and pulse until it forms a ball. Add more water if required. Form into a disc and wrap in plastic wrap. Chill for at least 1 hour.
Preheat the oven to 180°C (fan-forced). Roll pastry between 2 sheets of baking paper to ﬁt a Wiltshire Quiche & Tart Pan 23.5cm. Press pastry into tin and trim excess with a sharp knife. Prick base all over with a fork. Freeze for 20 minutes.
Line pastry with baking paper and ﬁll with Wiltshire Baking Beads. Bake on a baking tray for 12 minutes or until slightly golden. Remove baking beads and paper. Return to oven for a further 12 minutes or until golden and dry. Remove base from oven, and reduce the oven to 160°C.
Place cream, sugar and butter in a saucepan over medium heat. Bring to the boil then pour over chocolate in a heatproof bowl. Stand for 2 minutes then stir until smooth and combined. Add egg and salt ﬂakes and whisk to combine. Pour into cooked tart base. Place on a baking tray and bake for 20 minutes or until surface has only a slight wobble to it. Remove from the oven and set aside to cool. Once cooled, transfer to the fridge and chill for at least 2 hours if not overnight.
Remove from the pan before serving.
Use a melon baller to create small rounds of watermelon. Arrange on the tart with pistachios, berries and rose petals. Slice, serve & enjoy!