Remove kernels from corn cobs and scrape cobs to get any juices (milk). Reserve 1 cob.
Melt in a large pot or dutch oven over medium heat. Add onion and cook for 6 minutes until translucent. Add jalapeno and cook for 3 minutes. Add garlic and cook for 1 minute. Add corn, corn milk, corn cob and potatoes, cook for 10 minutes, stirring frequently. Simmer until potatoes are soft and soup starts to thicken, about 20 minutes. Remove and discard cob.
Season with salt and pepper. Serve. Garnish with cilantro.