TOASTED MACADAMIA NUTS (plan to do ahead of time): Roughly chop the macadamia nuts and then place in a saute pan over medium heat with the salt. Toast the macadamia nuts until golden brown and fragrant, making sure to stir frequently.
Once the macadamia nuts are toasted, combine the toasted macadamia nuts and nut milk (or water) in a bowl and cover with plastic wrap. Let the nuts soak for about an hour.
After the nuts have soaked for an hour, place the nuts and nut milk in a blender or food processor. Puree until smooth.
MACADAMIA NUT MILK (plan to do ahead of time): Using a cheesecloth or thin dish towel, strain the liquid from the puree. This is best done over a large bowl. Pour the nut puree over the cheesecloth and squeeze the liquid through the cloth. We want to get 1 cup of liquid from our puree. If you've strained as much as possible and still don't have 1 cup of liquid, place the leftover paste from the cheesecloth back into your blender or food processor, add another 1/2 cup of nut milk and puree again. You'll then strain the puree again to get more liquid.
The nut milk can be made up to a week before you plan to make the custard. Just make sure to refrigerate the milk in a mason jar or other airtight container.
FOR THE CUSTARD (plan to do ahead of time): In a medium-sized mixing bowl, whisk the sugar and egg yolks. Add the cornstarch and whisk until the mixture is light yellow and a bit thick.
In a medium saucepan, heat 1 cup of the nut milk and vanilla. Just before the milk begins to boil, remove it from the heat.
Very slowly, add the nut milk to the egg mixture, whisking constantly to avoid curdling the eggs. When you’ve combined all the nut milk with the egg mixture, pour the mixture back into the saucepan and return to the stove.
Cook the mixture over medium heat until it has thickened, about 10 to 15 minutes. Make sure to stir frequently. Allow the custard to cool completely and then place in an airtight container to refrigerate overnight.
TO COMPLETE THE MACADAMIA NUT CREAM FILLING (finish day of assembly): Beat the heavy whipping cream to stiff peaks. Fold the heavy whipping cream into your custard. Best used right away.