Arrange potato in a large 9 inch pan and set aside
In a med sauce pan add butter, cook til melted. Slowly add the flour whisk til combine and cook for about 1-2 minutes(don't turn brown). Slowly add the milk and whisk fast to avoid lumps, cook for about 2-3 until thicken a bit.
finally add 1 cup of cheese til little melted. Will finish in the oven.. Cook for 1 hour, then add the remaing cheese and cook till bubbly and cheeses is brown to your texture..