Butter a 9-inch springform pan and line the bottom with a parchment paper circle.
Cover the bottom of the pan with the cookies. Sprinkle 1/2 cup of the granola on top of the cookies. Scoop the peach ice cream and vanilla ice cream onto the granola layer, packing them 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 of it, 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 vanilla whipped cream frosting:
Add the heavy cream, confectioners' sugar and vanilla to a large bowl and whip with an electric mixer 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 vanilla whipped cream frosting and sprinkle with the remaining 1/4 cup granola. 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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