1. Cut the flesh off both sides of the mango stone. Scoop out the flesh and discard the skin. Set aside 1 piece of mango. Cut the remaining mango, including the flesh clinging to the stone, into chunks. Puree with the orange juice in a food processor. Transfer to a bowl and stir in the orange zest and superfine sugar.

2. Sprinkle the gelatin over 3 tbsp water in a small heatproof bowl and let stand for 5 minutes until softened. Place the bowl in a saucepan of gently simmering water and stir until the gelatin has completely dissolved. Cool slightly, then stir into the mango puree.

3. Whip the egg white and salt in a large, clean bowl until stiff peaks form. Fold the egg white mixture into the mango mixture.

4. Whip the cream to soft peaks. Fold half into the mango mixture. Divide the mixture among 4 dessert glasses. Refrigerate until the mousses are set, at least 1 hour or up to 2 days.

5. Slice the reserved mango. Top each serving with a dollop of whipped cream and a mango slice. Serve chilled.