Shuck and de-cob the corn. Place the corn in a zip lock bag or a bowl. Refrigerate until ready to use. Place the cobs in a soup pot. Cover with water and place over medium heat on the stove.
Purée corn to form a liquid, 1-2 minutes or more, depending on how powerful your blender is. In a medium pot, heat oil over medium-low heat. Add onions and sweat until translucent, about 2 minutes.