Toss the potatoes with the onion, celery, flour and salt, and pepper; set aside for about 10 minutes.

Meanwhile, melt the butter in a Dutch oven or soup pot. Add the potato mixture to the pot; stir to coat. Add enough water to cover the potatoes and bring to a boil; stir in the milk, reduce to a simmer, and cook, uncovered, stirring occasionally about 25 to 30 minutes, or until potatoes are tender. Taste, adjust salt and pepper and continue cooking on simmer, uncovered until the soup reach desired consistency and thickness. Garnish each serving with shredded cheese if you like and serve immediately.