Preheat the oven to 180°C (160°C fan oven) Gas Mark 4. Break the pastry into pieces and put into a food processor with the 50g of coconut. Pulse until the pastry is well mixed with the coconut. Roll out the pastry on a lightly floured surface until big enough to line a shallow, 22-23cm round loose-bottomed tart tin. Line the pastry with greaseproof paper, fill with baking beans and bake for 25 minutes. Remove the paper and beans and cook for 10 minutes more until sandy and golden. Set aside.
Lower the oven to 160°C (140°C fan oven) Gas Mark 3. Whisk together the eggs, sugar, cream and citrus juices. Sieve into a jug, then stir in the zest from 2 lemons and 2 limes.
Put the pastry case back into the oven, then carefully pour in the citrus filling – it’s easier than trying to carry it after filling. Bake for 30-35 minutes until the filling is just set. Leave to cool completely before serving at room temperature, or chilled from the fridge. Sprinkle with a little toasted coconut and the rest of the zests, then cut into thin wedges.