Preheat the oven to 200 degrees Celsius or 400 degrees Fahrenheit.
Line a baking sheet with greaseproof paper or a silicone sheet. Pour the sugar into a heavy-based, non-stick frying pan and set over a medium heat. Gently tilt and swirl the pan (do not stir) until the sugar has melted and turns a deep caramel colour.
Add the peanuts and coconut and stir to combine. Pour the mixture into the lined tray and leave to cool. When cool, break into shards and set aside.
For the mango tart, unroll the pastry and cut out a circle the same diameter as the pan you’re going to use. Heat the sugar and butter in a 20cm non-stick frying pan until the sugar has melted and turned a deep caramel colour.
Remove from the heat and leave to cool slightly. Add the mango wedges and shake gently until they start to caramelise. Remove from the heat then lay the pastry over the top.
Bake for 20 minutes until the pastry in risen and golden. Leave to cool slightly then turn out onto a plate. Serve the mango tart topped with shards of the brittle.