Cut acetate into two 3” high and 20” long strips.
Place a piece of parchment or silpat onto the counter and invert cake onto it. Peel off parchment/silpat from bottom of the cake.
Using the cake ring, stamp out 2 circles (start in the corners to be able to get 2 full ones). These will be your top and bottom layers. Stamp out 2 half circles from the remaining scraps.
Clean cake ring and place in the center of your quarter-sheet pan lined with parchment or a silpat.
Place 1 strip of acetate inside the cake ring to line it. **Make sure the cake ring is completely dry or you won’t be able to get it out of the ring after freezing!!**
Place your less pretty full layer into the bottom. Dip a pastry brush into the soak and brush onto the cake layer.
Using the back of a spoon, spread 1/5 of the frosting in an even layer over the cake.
Sprinkle 1/3 of the crumble evenly over the frosting. Press down with the back of your hand to anchor them in place. (I reserved the chunkiest crumbs for the very top).
Using the back of a spoon, spread 1/5 of the frosting in an even layer over the crumble.
With your index finger, tuck the second strip of acetate between the cake ring and the top 1/4 inch of the first strip of acetate, so that you have a clear ring of acetate 5 to 6 inches tall – high enough to support the height of the finished cake.
Place the two half circle cake pieces on top of the frosting layer and press in additional cake scraps to fill in the layer. Use the back of your hand to press the scraps together into a flat even layer.
Repeat steps 6, 7, and 8.
Place the remaining cake round onto the frosting and cover the top with remaining 1/5 frosting. Spread frosting evenly or a bit messier if you like.
Top with remaining crumble — either around the edge or in the center, however you like.
Place sheet pan into the freezer and freeze for a minimum of 12 hours. Cake will keep in the freezer for up to 2 weeks.
At least 3 hours before serving, remove the cake from the freezer and using your fingers and thumbs, pop the cake out of the cake ring. Gently peel off the acetate and transfer cake to platter or stand.
Let it defrost in the fridge or counter for a minimum of 3 hours (wrapped well in plastic, the cake can be refrigerated for up to 5 days).