Shuck the corn and score each row of kernels with a sharp knife. Use the dull side of the knife to scrape the pulp and corn milk from the cobs into a wide bowl. Pour the whole milk into a small saucepan over medium heat and bring to a low simmer.

Melt the butter in a 4- to 5-quart heavy-bottomed pot over medium heat. Add the onion, salt, and pepper, and cook, stirring often, until translucent, about 6 minutes. Stir in flour and corn and cook for 2 minutes. Add whole milk and bring to a simmer; the mixture will thicken. Serve hot, garnished with parsley.