For the cake: Preheat the oven to 300 degrees F.
Sift the flour together with 1/2 cup of the sugar and set aside.
Put the egg whites in the bowl of an electric mixer. Be SURE that the bowl is clean and dry, any fat in the bowl can prevent the egg whites from whipping up fluffy fluffy fluffy! Add the salt and the cream of tartar to the egg whites. Beat the egg whites on a medium-high speed until they reach soft peaks, about 5 minutes.
While the mixer is running, gradually add the remaining sugar. DO NOT plop the sugar in all at once or it will push the air out of the whites that we are trying to beat in. Add in the vanilla and zests and then stop the mixer. Add 1/3 of the flour/sugar mixture and fold gently fold, do this quickly but gently. Repeat the process 2 more times until all of the flour/sugar mixture is incorporated.
Transfer the cake batter into an ungreased tube pan. Bang the cake pan on the counter a couple of times to release any air bubbles trapped in the cake batter.
Bake the cake on a sheet tray in the preheated oven until it is light and springy, about 1 1/4 hours. Cool the cake for at least 1 hour before unmolding. Serve with the tropical fruit compote.
For the compote: In a food processor or blender, puree the coarsely chopped mango and 1/2 cup orange juice. If this mixture needs a little more sweetness, add in the 2 teaspoons of sugar and puree for another 10 seconds or until the sugar has dissolved.
Combine all of the fruit and remaining orange juice and let the mixture sit at room temperature for 20 to 30 minutes.
Serve slices of the cake drizzled with the mango puree and sprinkled generously with the fruit compote. Garnish with mint and serve.
Wow! How tropical-fruity and the cake is light as air!