Heat the oil and butter in a large pot over medium heat. Add in the diced onion, diced celery, diced pepper and diced potatoes. Cook the vegetables for about 10 minutes stirring occasionally until they just begin to soften.
While the vegetables are cooking cut the corm kernels off the cob. Add the corn, garlic, thyme, salt and pepper into the pot and cook for a couple of minutes. Add in the flour and stir to coat the vegetables. Cook for another 2-3 minutes.
Add the vegetable broth into the pot with the vegetables and bring it to a boil. Once it begins to thicken turn it down to a simmer and add in the milk. Simmer the chowder for another 10 minutes.