Realizing that I actually had all of the ingredients to make that dish, it was prepared and served on New Year's Day. 5 pounds of potatoes were peeled and sliced very thinly.
Sweet onions and 4 cloves of garlic were sauteed to caramelize the edges.
Then a stick of butter was melted in the bottom of a saucepan. To that I added about 3/4 of a cup of flour to make a "roux". Once the flour and butter were smoothed together, milk could slowly be added to the pan and blended without lumping. 3 cups of milk seemed about the right amount.
I sprayed the bottom of a very large casserole pan with Pam and started to layer the ingredients: white sauce, potatoes, ham, onions and cheese, winding up with four layers. Over all of this, I poured the remaining sauce which had by now thickened quite a bit. Panicking, I poured a can of evaporated milk over all so that it wouldn't be too thick, but creamy.
In the past, I have noticed that it takes a long time to get the potatoes to soften in the oven. The friend that I obtained the recipe from cooks this casserole for four hours at 325! I cooked it for one and one half hours at 350 and the potatoes were great. My version was a tiny bit soupy although very flavorful! We could have lived without that last can of milk. At the same time, it wasn't too dry which is never good. This is no diet food- it is a homey "comfort" food. We all enjoyed this tasty dish which was labor intensive to make and therefore very special for a holiday meal.