18 large poorly risen macaron shells (or enough to make three layers in each mould)
Sprinkles - optional
If using tart rings, cling film the base of each, twisting to secure around the edge and creating a taut surface - this will become the top of the ice cream cakes so you want them to be smooth. Place cling side down onto a baking tray and line each with acetate - this step is optional but will make it easier to remove once frozen.
Pour some ice cream mixture into the moulds, filling about 1/3 of the way, followed by a layer of macarons. Repeat with remaining ice cream mixture and finish with a layer of macarons, pressing them in to create a flat surface. Freeze until solid - at least 5 hours or overnight.
Remove ice cream cakes from freezer. Remove from tins/rings and flip onto a clean tray or plate. Peel away acetate if using. Decorate as desired and return to freezer until ready to serve.