Preheat the oven to 400 degrees F.
Slice the corn kernels off the cobs. On a sheet pan, toss the corn and the whole poblano pepper with 1 tablespoon olive oil, 1 teaspoon salt and 1/2 teaspoon black pepper. Spread the corn into an even layer across the pan.
Brush any corn off the poblano pepper and put it on a piece of aluminum foil directly on the rack next to the pan with the corn. Roast the corn and the poblano pepper for 25-30 minutes. Flip the poblano pepper to the other side halfway through roasting. The corn should be bright yellow, golden and lightly browned. (Reserve 1/3 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.
Warm 1 tablespoon olive oil in a large saucepan over medium heat.
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, peppers, coconut milk, vegetable broth and 1/2 teaspoon salt and 1/2 teaspoon black pepper. 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 as necessary.
Divide the soup into bowls and garnish with the reserved corn, sliced scallions and black pepper.