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Line a 9" springform pan with a parchment round (for easier serving) or leave the pan bare.
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To make the crust: In a food processor, process the Biscoff cookies into fine crumbs. With the machine running, stream in the melted butter until the mixture is damp and holds together when squeezed. Scoop out about 1/2 cup (77g) of the cookie crumbs and set aside. Transfer the remaining crumbs to the prepared pan and press into an even layer with your fingers or the bottom of a flat measuring cup. Set aside.
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To make the ice cream: In a large bowl, whisk together the mango pulp and lime juice. Set aside.
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In the bowl of a stand mixer fitted with the whisk attachment, beat the heavy cream, condensed milk, vanilla, and salt on medium speed until medium peaks form.
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Transfer about 2 cups (about 360g) of the whipped cream mixture to the bowl with the mango and lime. Working by hand, use a whisk or the whisk attachment to gently fold the whipped cream into the mango mixture until combined. To the remaining cream in the mixer, add the toasted coconut and fold to combine.
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To assemble the mango float: Transfer about half of the coconut-whipped cream mixture (about 1 1/4 cups or roughly 250g) into the pan and spread to the edges. A small offset spatula is especially helpful here.
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Sprinkle about half of the reserved cookie crumbs over the top.
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Transfer the mango-whipped cream mixture to the pan and spread it evenly over the top of the coconut-whipped cream. Evenly distribute the remaining cookie crumbs on top of the mango layer.
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Spread the remaining coconut-whipped cream mixture over the top of the mango layer, and evenly spread it to the edges.
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To finish the mango float: Slowly pour the mango pulp on the top of the cake in a swirl pattern. With a toothpick or chopstick, swirl the mango to create a marbled effect. Cover with plastic wrap or your favorite reusable wrap, and freeze until firm, at least 6 hours, or overnight.
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To serve, transfer the ice cream to the refrigerator for about 1 hour. Release the sides of the springform pan from the cake. If not serving the whole cake, use a hot knife to slice the cake into portions and return the remainder to the freezer. For the best texture, let individual slices sit at room temperature for 5 to 10 minutes before enjoying.
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Storage information: Store leftover ice cream cake in the freezer, well-wrapped, for up to 2 weeks.