After cutting corn from kernels, scrape the cob using the dull side of the knife to collect the sweet milky liquid at the base of the kernels. Toss corn kernels to separate them and make sure no corn silk remains.

Place half of the the kernels in a saucepan and half in the bowl of a blender. Add cold water to the blender. Blend on highest setting until completely smooth, 1 or 2 minutes. Pour mixture into saucepan containing the rest of the corn. Place pot on medium-high heat and bring to a simmer. Season with salt and cayenne pepper. When mixture begins to simmer, stir and reduce heat to medium-low.

Continue to simmer about 30 minutes, stirring occasionally. Reduce heat to lowest setting and add butter. Using an immersion blender, mix soup in several pulses until butter emulsifies into the soup and mixture comes together and looks creamy, about 30 seconds.