Preheat the oven to 180°C and spray a 21 cm round cake tin with non-stick spray.
Pour the syrup into the cake tin and heat in the oven for about 2 minutes. Remove and tilt the tin to evenly spread the syrup. Lay the mango over the syrup and set aside.
In a large mixing bowl, cream the butter and sugar until light and fluffy. Beat in the eggs one at a time beating well after each addition. Fold in the flour and enough milk to form a smooth lump-free batter.
Spoon the mixture over the mango slices and smooth to level out. Bake until golden, for about 40 minutes. Leave to cool before carefully inverting the cake onto a serving dish and serve with whipped cream if desired.