Place the cashews, 1/4 cup macadamia oil (or other neutral tasting oil of your choice) and salt in the container of your high-speed blender.
Process on medium-low speed for about 30 seconds, until the nuts are reduced to a thick paste. Slowly increase the speed to medium-high and continue processing for another minute or so, pushing down with the tamper as needed, until the nut butter starts to run freely with the blades.
At this point, increase the speed all the way up to high and process for another minute, until the nut butter is really creamy.
If you find that your nut butter is still a little too stiff, adjust the consistency by adding a little bit of oil, one tablespoon at a time. Process until the oil is fully incorporated before adding more.
When your cashew butter has reached the desired consistency, transfer it to a clean glass jar and store in a cool dry place for up to several weeks.