Butter a 9-inch springform pan and line the bottom with a parchment circle. Cover the bottom of the pan with the pound cake, using any extra pieces to line the sides of the pan if desired. Scoop the mango and passion fruit sorbets onto the pound cake, packing it in tightly and alternating the scoops to create a marbled or checkerboard effect. Spread with an offset spatula to make a smooth top. Cover with plastic wrap and freeze until firm, 2 to 2 1/2 hours.
Unmold the cake by running a knife around the edge, then unhinge the springform and remove. Invert the cake onto a sheet of plastic wrap and remove the bottom of the pan and the parchment. Place a plate on the bottom and invert once more.
For the whipped cream frosting:
Add the heavy cream, confectioners' sugar and vanilla to a large bowl and whip with an electric mixer on medium-high until soft peaks form. (This makes enough frosting to cover the top and sides of the cake with additional to pipe decorations if desired.)
Frost the top and sides of the cake with the whipped cream frosting and drizzle with the caramel sauce. If the cake begins to get too soft, put it back into the freezer for a few minutes.
Freeze another 1 1/2 to 2 hours or overnight. Before serving, let the cake sit at room temperature for about 20 minutes.
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