In a medium bowl, mix together the milk and vinegar. Allow to sit aside for about 5 minutes.
In the meantime, in a small bowl, melt the butter in the microwave until it is just about melted (about 30-45 seconds). Whisk in the maple syrup while it is still warm. Mix in the vanilla.
In a large bowl, mix together the flour, oats, baking powder and salt. Make a well in the dry ingredients, and slowly add in the milk mixture and the butter mixture. Whisk together until everything is mixed and the batter has come together.
Pour or scoop the waffle batter into a hot waffle iron (I used a ¼ cup measuring cup for each waffle, but waffle makers vary). Cook waffles for about 4 minutes each, until cooked through. Once done, transfer the waffles to a cooling rack.