Cut the corn into thirds and shave off the kernels with a knife. Mince the onion.

Heat butter in a pot over medium heat. Add corn and onion, sauté until the onion softens, then cover and steam on low heat for 3 minutes.

Add water and bring to a boil. Cover and simmer on low heat for about 15 minutes. Reserve 1 tbsp of corn for garnish.

Transfer the mixture to a heatproof container and blend until smooth using a blender.

Return the blended mixture to the pot, add milk, and warm through. Adjust seasoning with salt.