Heat oven to 200C/180C fan/gas 6. Butter a 22cm round loose-bottomed tart tin, then use the sheet of pastry to line the tin. Prick the base with a fork, then lay a sheet of baking parchment on top and fill with baking beans. Bake for 20 mins. Remove the beans and baking parchment and cook for a further 5 mins. Remove from the oven and leave to cool.
To make the custard, put the milk, custard powder, sugar and vanilla extract in a pan on a medium heat and keep stirring until smooth and thick, around 5-10 mins. Leave to cool and cover with cling film to stop a skin forming.
Once the base and custard have cooled, spread the jam over the pastry and sprinkle with half the coconut. Pour in the custard, then sprinkle with the remaining coconut and chill. Decorate with raspberries and a final sprinkle of coconut, and serve.