Place oats in a medium bowl and cover with water. Soak oats 8 hours or overnight.
Once oats have completed soaking, drain and rinse with clean water. Place oats and 1 cup fresh water in a small pan. Bring to a boil. Lower heat and simmer until oats are soft, about 35-40 minutes. Check water level as the oats cook. If they begin to dry out, add ½ cup water, and continue to cook. Turn off heat, and allow oats to cool.
Place cooked oats and their cooking liquid in a blender, and process until smooth. Pour mixture through a fine sieve, and press solids to extract all the liquid. Reserve solids for another use. Add maple syrup and vanilla to oat milk, and stir to combine.
Refrigerate in a covered container until ready to use.