Slice the kernels off the corn cobs, then use the back of a chef’s knife to scrape off the milky liquid that’s left on the cob. Snap the cobs in half and set aside. Heat the butter in a large pot or Dutch oven over medium heat. Add the onion, celery, and red pepper and cook, stirring occasionally, for 8 minutes, or until softened. Stir in the garlic, then add the water, potatoes, Old Bay, salt, thyme, paprika, bay leaf, cayenne, several grinds of pepper, and the corn cobs. Simmer for 20 minutes. Remove and discard the corn cobs and bay leaf. Add the corn kernels and milky corn liquid to the pot and simmer for 10 to 15 minutes, or until the potatoes are tender. Transfer 2 cups of the soup to a high-speed blender and add the cashews. Blend until creamy, then stir the mixture back into the soup. Stir in the lemon juice and season to taste. Garnish with chives and serve with dollops of sour cream, if desired.