Peel potatoes and cut into 1 to 1½ inch pieces.Put in sauce pan, cover with water, and bring to a boil.Lower the temperature, then boil 15 minutes or until potatoes are just softening, then drain. Potatoes need to be firm so they aren't crumbling.In a small skillet, melt butter.Add in flour, stirring until smooth.Mix in milk gradually until there is no clumping.When sauce begins to thicken, stir in grated cheese until melted and thoroughly blended.Place potatoes in serving bowl, then pour cheese sauce over potatoes.Serve immediately.