Weigh out the raw cocoa butter. This is the best way to make chocolate, to weigh the ingredients, so the texture turns out accurately.
Without a scale version: You will need to heat the cocoa butter on its own first either over a double boiler or the microwave. Heat 1 minute, stir in between every 30 seconds until almost melted. Whisk until completely smooth. Make sure your other ingredients are not cold or it will cause the cocoa butter to harden bits throughout.
With a scale version: Add the milk and cocoa butter to a microwave-safe bowl. I do the microwave for 1 minute and then 30 second intervals, stirring in between, and just until about 90% melted. You need to be careful not to overcook or burn the cocoa butter. Alternatively, you can melt it over a double boiler.
Once the cocoa butter is almost all melted, whisk until it is completely smooth and there are no more floating pieces left.
Add the room temperature cashew butter, milk (if using the non-scale version), agave, vanilla, powdered sugar and salt and whisk until completely smooth. Blend it in a food processor if needed. It needs to be completely combined or the cocoa butter fat will separate in the fridge. If any bits of cocoa butter seize up, just reheat the mixture for a few seconds.
Place the bowl in the fridge for 3-4 hours or until completely firm all the way to the center. It should be hard. Leave to sit at room temperature until soft enough to use a cookie scoop to scoop and roll into balls.
Roll each ball into your desired ingredients. Powdered sugar is the prettiest and most traditional coating, but you could also do chopped nuts, like crushed pistachio nuts for a beautiful color. Store at room temperature and they will retain their perfect truffle texture.
Notes
CASHEW BUTTER: The purpose of using raw cashew butter instead of other nut butters is for many reasons. Cashew butter is lightest in color, most neutral in flavor and is naturally sweet. Using something like almond butter would not only make it much darker, but would have a strong nutty taste, so it won't really work with another nut butter, except maybe something like macadamia. However, macadamia nuts are stronger in nutty flavor. Also, raw is important as it's only cashews. Roasted has oil added almost always and is much stronger in flavor and color, so it is not recommended.
MILK: I've tested this both with homemade cashew milk and canned lite coconut milk (Sprouts brand) and both work. Just make sure to use a creamy milk for the best results.