1. Line a 20cm square tin with parchment paper and set aside.
2. In a jug, heat 125ml of water with the juice and zest of one lime. Stir in the gelatine until completely dissolved and set aside in a warm place.
3. In a pot set over a medium-high heat, stir together the caster sugar, golden syrup, the juice of the remaining lime and 125ml of water. Checking with a thermometer, heat to 120-130˚C, or check by dropping some of the syrup into cold water to see if it forms a rigid ball.
4. Once the mix has reached the right temperature, whisk in the dissolved gelatine mixture and set aside.
5. In a large bowl, whisk the egg whites to soft peaks. While the mix is still whisking, stream in the hot liquid slowly and continue whisking until very stiff.
6. Pour into the prepared tin, sprinkle over the desiccated coconut and allow to set for eight hours or overnight.
7. Once set, cut into cubes.

Per serving: 107kcals, 2.1g fat (1.6g saturated), 22.1g carbs (20.6g sugars), 2g protein, 0.6g fibre, 0.012g sodium