Freeze ice cream in a baking tray for an even from which to slice and stamp shapes. To remove the ice cream, invert the tray and wrap it in a warm tea towel.
Mark out the positions for all the cuts on the slab, then apply even pressure on to the knife. Rinse the knife in hot water between each cut.
Cut the strips in one direction, then in the opposite direction. Take care not to move the strips as you work - this will result in misshapen diamonds.