Rinse cashew nuts a few times, then soak them with clean water overnight. Drain.
Put 1 cup of soybean into a blender, then add 3 cups of water (the ratio is 1:3).
Process on high speed until the mixture is very fine, then strain through a colander lined with a coffee cloth (or cheesecloth).
Hold up the cloth and lightly squeeze out the milk.
Repeat the same for the remaining cashew nuts.
Strain the cashew nut milk through the cheesecloth again into a large microwave-safe glass bowl.Cook (WITHOUT lid or it will spill) on high in the microwave (1000 W) for about 45 minutes or until boiling, then continue to boil for another 1-2 minutes.
Remove and set aside to cool for a while. Sweeten to taste with sweetener and serve either warm or cold.
Keep refrigerated for up to 3 days.