Gather all the ingredients. Preheat the oven to 450ºF (230ºC). For a convection oven, reduce cooking temperature by 25ºF (15ºC).
Slice off the corn kernels.
Place the corn kernels on a rimmed baking sheet, saving the cobs for later.
Add olive oil, sprinkle of kosher salt, and paprika.
Mix all together with your hands and spread out evenly in a single layer. Roast the corn kernels at 450ºF (230ºC) degrees for 15 minutes. Once it's done, remove it from the oven and set it aside till Step 8.
Meanwhile, thinly slice the onion against the grain. Heat the butter in a heavy-bottomed pot (thicker at the base so it absorbs and distributes heat better).
Add the sliced onion and pinch of kosher salt and sauté until translucent.
Add the roasted kernels and water.
Add the reserved cobs in the pot as they naturally sweeten the soup. Push the cobs down to see if they are covered with water. If not, add more water.
Bring to a boil over medium heat. Cover and lower the heat to medium-low heat and simmer for 15 minutes. During this time I highly recommend skimming the foam on the surface for more refined taste. After 15 minutes, discard the cobs.
Using an immersion blender, blend the soup until creamy and smooth. If you use a food processor or blender, let the soup cool for a few minutes before you start blending to avoid major splashes. Make sure to cover the hole with a towel when blending.
If you want to make your soup similar to corn potage (Japanese corn soup), strain the soup through a fine-mesh sieve for a smoother consistency.
Transfer the soup back to the pot and add heavy cream and milk. The ratio is entirely up to you. Here I used equal parts of milk and heavy cream, 1 cup each. Bring back to a simmer and cook uncovered for 10 minutes or more, stirring frequently. Once the water evaporates and it’ll be more flavorful.
Add kosher salt and freshly ground black pepper. Make sure to taste the soup when you season. Finely chop parsley. Serve the soup hot or chilled. You can drizzle olive oil and/or heavy cream and sprinkle the parsley to garnish.
You can keep the leftovers in an airtight container (or in the pot) and store in the refrigerator for 3 days and in the freezer for 2-3 weeks.