Add the coconut milk and cream to an airtight container and add half a tonka bean to the liquids. Cover and allow to infuse in the fridge for a few hours, or overnight. This is optional, but adds more flavour.
Remove the tonka bean from the liquids and whisk all the ingredients together in a bowl, or blender.
Pour into one large mason jar and place the lid on the jar. Tighten enough to allow air to escape, without allowing water to enter the jar.
Submerge in heated water bath and cook for 60 minutes.
Remove when time is up and allow the jar to cool for a few minutes. While cooling, prepare a bowl with ice and water. Submerge the cooled jar in the ice bath. Place in the refrigerator to chill.
Serve:
Mix the sugar and spices and spread on a plate. Moisten the glass rim and dip the rim in the sugar mix.
Fill with eggnog and top with grated tonka bean or nutmeg.