To roast the corn on the cob, preheat oven to 450 degrees. Remove the outer husk of the corn, leaving just a few layers. Place the cobs on a baking sheet and place in the oven to roast for 40 minutes. When done, remove from the oven and cool slightly before removing the remaining husk and silk and slicing corn of the cob.
In a medium sized pot add the potatoes, celery, carrots, corn, vegetable stock and thyme and bring to a boil. Turn down to a simmer and cook until the vegetables are tender.
Meanwhile, in a small pot, melt the butter and saute the onion for a few minutes until soft and translucent. Add the garlic and cook for just a minute. Add in the flour and whisk together, cooking over medium heat for a minute or two before adding the milk. Whisk until smooth and cook until thickened. Turn off the heat.
When the vegetables are tender add the thick, creamy mixture and stir together. Add salt and pepper to taste and serve topped with some fresh green onions or parsley on top with your favorite bread or biscuits.