For Mango Curd
Kiwi, passion fruit, guava, dragon fruit, pomegranate, pineapple, papaya or whatever is available in season.
For cake, preheat oven to 350 °F. Grease and sugar a 9-inch cake pan.
Cream butter and sugar until smooth. Add vanilla and eggs, one at a time, beating well after each addition. Stir in sour cream and pineapple. Ina a separate bowl, sift flour, baking soda and salt and gently stir into butter mixture. Scrape into prepared pan and bake for 40 to 50 minutes, until a tester inserted in the center of the cake comes out clean. Cool for 20 minutes, then turn out onto a plate to cool completely.
For mango curd, whisk mango purée, lime juice, sugar, yolks and eggs in a bowl over gently simmering water until thickened and coats the back of a spoon, about 10 minutes. Remove from heat, strain and let cool to room temperature. Using an immersion blender, purée butter and mascarpone into curd (both butter and curd should be at the same temperature). And chill for at least 3 hours.
To assemble cake, slice cake into 2 layers. Spread half of curd on bottom half and top with second cake layer. Top with remaining curd and arrange fresh fruits on top. Serve within 2 hours of arranging fruit.