Preheat the oven to 350 degrees. Coat a 2 quart baking dish with non-stick spray, set aside.

Prepare your potatoes - wash and peel if desired. Slice in ⅛ inch or close to size slices. Set aside.

In a large saucepan, melt the butter over medium/low heat.

Add in the onion and cook for about 2 minutes or until the onions are transparent and soft.

Meanwhile, mix the sliced potatoes with the diced ham and place in your prepared baking dish. Set aside.

Sprinkle the flour and salt and pepper over the onions. Stir to coat - it will be clumpy, that's normal.

Add in the milk and continue to heat. Bring the mix to a boil and cook for an additional minute to thicken the sauce.

Pour the sauce over the potatoes and spread evenly to the edges.

Cover the baking dish with foil and cook in the preheated oven for 30 minutes.

Remove the foil and continue to cook for an additional 1 hour to 1 hour and 10 minutes or until the top is golden brown and the potatoes are tender.

Allow to cool slightly before serving.