I have made mini ice cream cakes before, but never a big cake. Part of the reason was I didn't have a springform pan. But now I do and it was very easy to put together.
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I spread the first layer onto the crushed cookie and sent it back to the freezer.
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We tried a couple stabilized whipped cream methods with no luck. In the morning I tried one more time with gelatin. I used cold water and gelatin, then used the microwave to dissolve it further in very small bursts. It cooled as I whipped the cream.
After adding the gelatin, the whipped cream looked different for me, but tasted ok. I placed it in the fridge while I took the cake out of the springform ring. After releasing the ring, I took a spatula warmed in hot water and gently cut around the cake edge.
I could probably use any kind of whipped cream to cover the cake as it freezes almost immediately. I wanted the use the stabilized whipped cream to pipe on the cake and it seemed to work pretty well. Once I got going on the frosting, I did return it to the freezer between steps, but generally worked quickly. I had to let the cake thaw a little in order to press the m&m's into the cake. I wish I had spaced the m&m's a bit better, I'll know for next time.
I had enough whipped cream frosting to cover the cake with a thin layer and color some purple and decorate. There's a bit of white saved for any cake mishaps too.
To preserve this cake for a week in the freezer, I needed some sort of box. The base of my cake holder is too big to fit in my freezer. What I ended up doing was placing the cake on a 10" cake board. Then I put two pieces of aluminum foil spread out on a dinner plate. I placed the cake on the plate, then put the cake holder cover on top. The cover just fit over the bottom plate edge. Then I took the excess foil and wrapped it over the cover edges. Hopefully that will be protected well in the freezer until the party!