• Preheat. Preheat the oven to 400 °F

Sauce

• Cream. Measure the heavy whipping cream.
• Starch Slurry. In a small bowl, mix the corn starch with 1/2 cup of the heavy whipping cream until smooth and there are no lumps. Add the slurry back to the remaining whipping cream.
• Seasonings. To the heavy whipping cream, add the salt, ground black pepper, old bay, and powdered mustard. Mix well.

Casserole Components

• Ham. Cut the ham into small cubes.
• Green Onion. Thin slice the green onion.
• Potatoes. Scrub the potatoes well and remove any eyes. I am leaving the skins on, but feel free to stop here to peel. Then, thin slice the potatoes using a knife, food process with a mandoline blade or a mandoline slicer.

  Note: The potatoes will start to oxidize and turn brown. If you want to avoid this, put the potatoes in a bowl of water until ready to use. I don't mind, so I'm just going to slice my potatoes and set them aside.

Dish

• Grease. Using a paper towel, smear 1 Tablespoon of butter around the bottom and sides of a 9x9 casserole dish.

Assembly

• Drain. Drain the potatoes well. if needed, place them on paper towels to dry them better.
• First Layer. Place half of the potatoes in the bottom of the casserole dish. Then, top the potatoes with half of the ham and green onions. Give the layer a little press to compact everything down. Then add 1/2 the sauce. Finally, top with cheese.
• Second Layer. Layer the remaining potatoes. Then, top the potatoes with the second half of the: ham, green onions, and sauce. Top the potatoes with the remaining cheese.

Baking Round 1

• Bake. Cover the potatoes with foil. Bake for 45 minutes.

Baking Round 2

• Bake. Remove the foil and bake for another 30 minutes.
• Cool. Allow the potatoes to cool slightly before serving.