Preheat the oven to 180°C (fan).
In a large mixing bowl, rub together the flour, 3 tbsp sugar and unsalted butter until a crumb consistency is achieved. Add in the cold water and bring together to form a dough.
Tip the dough out onto a lightly floured work surface and cut off a third, set it to one side.
Roll the dough out, big enough to line the tart tin, drape it over the tin, folding and pushing the pastry into the corners. Leave any excess to hang over the edge. Prick the base all over with a knife.
Roll out the remaining third of dough, and cut out some stars, placing them on a lined baking tray.
Place both the tart case and stars in the oven and bake for 20-25 minutes until lightly golden. The stars may not need as long so keep an eye on them.
Once the case is baked, make the custard filling by whisking together the custard powder with 40g sugar and a splash of milk to form a paste. When there are no lumps, add the remaining milk and place over a medium heat and continue whisking until you have a nice thick custard. Pour it immediately into the tart case, spread evenly and allow to cool to room temperature before placing in the fridge to cool completely.
When the custard is cool and set firm, spread Bonne Maman Strawberry Jam over the top and pop back in the oven for 15- 20 minutes until the jam just begins to bubble. This will set the jam.
Allow the tart to cool slightly before placing the pastry stars on top and dusting with icing sugar and serving.
