Place the butter and sugar into a bowl, and whisk until smooth and creamy. Add the eggs, one at a time, beating well after each addition. Use a spatula to fold through the flour and coconut, then the mango pieces and yogurt. Scrape the mixture into your tin and smooth over the surface, then sprinkle with a little extra coconut. Bake for 30 mins until risen and golden and a skewer inserted into the centre of the cake comes out clean. Cool for 10 mins in the tin, then transfer to a wire rack. This cake is delicious served warm with an extra blob of coconut yogurt, or just as good cold. Keeps in a tin for up to 3 days.