Add the powdered milk to your food processor (or Mason jar). Then add the water, oil and salt.

Blend (or shake) for a few minutes and then check to see if it's starting to thicken. Keep blending until it starts getting really thick (remember, you're aiming for butter consistency). Check on it ever couple minutes to see if it's getting there.

After a few minutes it should be pretty thick, like butter or margarine. It might not be as thick as you're used to with butter or margarine, but that's also what makes it extra spreadable!