Preheat a soup pot over medium high heat. Sauté diced onion in oil with a pinch of salt until translucent, about 5 minutes. Add garlic and red pepper flakes and sauté for another minute. Add corn and carrots and cook for 10 more minutes over medium heat.
Measure one cup of the broth or water into a measuring cup. Mix in the cornstarch (or juices from frozen corn) with a fork until dissolved. Set aside.
Add remaining 3 cups of broth or water to the pot, along with the chopped potatoes. Cover and bring to a boil. Once boiling, if you're using fresh corn, break the corn cobs in half and add them to the pot. Lower heat to a simmer and cook for about 15 minutes, or until vegetables are tender. Remove and discard corn cobs. Add the one cup of reserved vegetable broth- starchy mixture, and cook to thicken, about 3 minutes. Add a splash of milk or cream, black pepper, salt to taste and lime juice.
Blend about half of the soup until smooth then add back to the pot.
Taste for salt and seasoning. Serve garnished with fresh corn kernels, chopped heirloom cherry tomatoes, diced jalapeños and fresh herbs.