Preheat the oven to 350˚F. Grease a 9 inch springform pan.
Mix the topping ingredients together and set aside.
Beat 1/2 cup butter and white sugar together in a large bowl with an electric mixer until soft and fluffy. Add the egg and vanilla and mix well.
In a medium bowl, mix the flour, baking soda, baking powder, salt and nutmeg. Slowly add the dry ingredients to the wet ingredients, alternating between flour mixture and buttermilk until fully incorporated. Fold in the mango and cherries.
Pour the batter into the prepared pan and sprinkle with the prepared topping.
Bake for around 20 minutes, or until a toothpick inserted comes out clean. Let cool on a wire rack