Preheat the oven to 400°F.
Cut the kernels off the ears of corn and place evenly on a parchment lined sheet pan. Toss corn and the whole poblano pepper with 1 tablespoon olive oil, 1 teaspoon salt and ½ teaspoon black pepper.
Place the sheet pan in the oven with the poblano pepper next to it on a piece of aluminum foil right on the rack. Roast the corn and the poblano pepper for 30 minutes. Flip the poblano pepper over halfway through roasting. The corn should be bright yellow and golden. (reserve ⅓ cup corn for garnish.) The pepper will be wrinkled and bubbled.
Put the pepper in a bowl and cover it. Wait 10 minutes before rubbing off the skin using a towel. Remove the seeds and roughly chop the pepper.
In a large saucepan over medium heat, add 1 tablespoon olive oil. Sauté the onions until they start to soften, about 3-4 minutes. Then add the potatoes and continue sautéing for another 2-3 minutes. The potatoes should begin to break up. Add the garlic, cooking for 30 seconds more until fragrant.
Add the corn and peppers to the pan with the coconut milk, vegetable broth and ½ teaspoon salt and ½ teaspoon black pepper. Bring to a simmer for 10-12 minutes until the potatoes are tender and cooked through.
Carefully transfer 75% of the soup to a blender to puree. Then pour it back into the pan to reheat.
Divide the soup into bowls and garnish with the reserved corn and sliced green onions. Season to taste with flaky sea salt and black pepper.