Soak the pistachios in a bowl covered with 4 cups of water for at least 8 hours or overnight.

After soaking, drain and rinse the pistachios under cold water.

In a blender, combine the soaked pistachios with 4 cups of fresh water and blend on high speed for about 1-2 minutes until smooth and creamy.

Place a nut milk bag, cheesecloth, or fine mesh strainer over a large bowl or pitcher. Pour the blended mixture into the strainer, allowing the liquid to pass through.

Squeeze or press the solids to extract as much liquid as possible.

If desired, return the strained milk to the blender and add maple syrup and vanilla extract. Blend briefly to combine.

Transfer the pistachio milk to a clean glass bottle or jar and store it in the refrigerator. Shake well before using.