Add all of the ingredients to a high-speed blender and blend on highest setting for 1-2 minutes if using cashews, or about 30 seconds if using pre-made milk. The mixture should be completely smooth.
Heat over medium-high heat. Stir constantly with a whisk until the mixture has thickened (3-5 minutes). When it sticks to the whisk it should be good to use on pizza.
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Notes
If you prefer not to make homemade cashew milk, simply substitute the 2 tablespoons of cashews and 1/2 cup of water with 1/2 cup of any plain, non-dairy milk.