Freeze the macadamia cremeux in a 6-in/ 15-cm cake pan lined with plastic wrap until solid, 6 hours or overnight. Unmold from the pan and trim to a 5-in/13-cm circle. Keep frozen until needed.
Using a pastry bag fitted with a #4 plain pastry tip, pipe the japonais batter into a 5-in/13-cm round onto a parchment-lined sheet pan.