Combine 1 cup water and 1 cup caster sugar in a saucepan and stir over low heat until sugar has dissolved, then bring to the boil and simmer for 5 minutes. Remove from heat, cool to room temperature, then stir in 1 tbsp lemon juice and 2 tsp rosewater. Combine 2 large ripe mangoes (peeled and cut into 2cm cubes) with 1 punnet strawberries (hulled and halved) and 1 punnet blueberries in a bowl. Cover and chill. To serve, divide fruit between four serving glasses and drizzle with rosewater syrup. Top with a scoop of vanilla bean ice-cream.