Homemade Potato Soup

russet potatoes , peeled and cut into large chunks (about 1-1/2 inch)

chopped sweet onion

chopped celery

all-purpose flour

Kosher salt and freshly cracked black pepper ,

to 1/2 cup (1/2 to 1 stick) salted butter

Water to cover

evaporated milk

Shredded cheese , for garnish, optional