1Melt butter in a large saucepan over medium heat; cook and stir onion until tender, about 5 minutes. Stir in corn, water, hash brown potatoes, black pepper, and salt. Bring to a boil; cover and simmer for 5 minutes.
2Whisk 1/2 cup milk and flour in a small bowl until smooth.
3Pour milk mixture into the saucepan. Stir in remaining 1 1/2 cup milk; cook, stirring frequently, until thick, about 5 minutes.