Remove your ice cream from the freezer about 10 minutes before you assemble your cake.
When you are ready to assemble, line the base of a 9-inch springform pan with parchment paper. Sprinkle crushed meringue all over the base of the pan. Spread half of the ice cream all over the base of the pan, pushing on the ice cream to ensure you have no gaps or air bubbles. I find it useful to drop small balls of the ice cream all over the meringue so you are not pushing the ice cream around too much. Smooth the top of the ice cream with a spatula so it is level. Once the ice cream is evenly spread out, crush more meringue over the top, gently pushing into the ice cream until the top is completely covered. Transfer to the freezer and chill for at least one hour.
Remove from the freezer and spread the remaining ice cream over the meringue, pushing down as you do, and using a spatula to create an even surface. Crush and sprinkle some more meringue over the top, again gently pushing the meringue just slightly into the ice cream. Return to the freezer and chill until ready to serve.
When ready to serve, lightly dust the top of the cake with cocoa powder. Unmold from the springform pan and transfer to a cake plate. Serve immediately.