Fill a large pot with water and bring it to a boil. Drop the corn into the boiling water and cook for 5 minutes. Drain, and rinse the corn under cold water. When it is fully cooled, cut the kernels from the cob and set aside.
Melt the butter in a saucepan. Add the onion and sauté over low heat for 5 minutes. Then add the flour, stir well, and cook another 5 min