How to Make It
Place oats in a medium bowl; add enough water to cover oats by about 1 inch. Let sit for exactly 15 minutes. The oats will look hydrated. (Do not exceed 15 minutes or the oat milk will become slimy.) Drain oats in a fine-mesh strainer; discard soaking liquid. Rinse oats in strainer under cold running water until water runs clear, about 30 seconds.
Combine drained oats, maple syrup, vanilla extract, salt, and 4 cups water in a blender. Process until smooth, about 1 minute.
Rinse the fine-mesh strainer and set over a large bowl. Pour processed oat mixture through strainer, stirring to help extract liquid. Discard solids in strainer, and strain twice more (without stirring).
Transfer strained oat milk to an airtight container, and chill until cold, about 15 minutes, before serving.
Oat milk will keep in the refrigerator for up to 1 week.