1-First Step: Prep and mise en place Preheat your oven to 350 degrees Fahrenheit. Butter a large casserole dish so the potatoes and sauce do not stick. Wash 3 pounds of russet or Yukon Gold potatoes thoroughly, then slice them very thinly, about 1/8 inch thick, using a mandoline or a very sharp knife. Thin slices cook faster and give the casserole that classic tender-but-hold-shape texture.

2-Second Step: Cook the onion and ham Heat 2 tablespoons butter in a large skillet over medium heat. Add the chopped yellow onion and cook for 1 to 2 minutes until translucent. Stir in 3 cups diced ham and cook 3 to 4 minutes until heated through. Remove from heat and set aside. This step builds flavor and warms the ham so it layers nicely between the potatoes.

3-Third Step: Make the cream sauce In a microwave-safe container, warm 1 1/2 cups half-and-half and 1 1/2 cups heavy cream for about one minute, just until no longer cold. Whisk in 1/4 cup flour and black pepper to taste until fully combined and smooth. Avoid adding much salt since the ham and cheeses provide saltiness; add sparingly if needed.

4-Fourth Step: Combine the cheeses In a bowl, combine 1 cup grated cheddar cheese and 1 cup grated Monterey Jack cheese and set aside. These cheeses give a balanced sharp and melty finish to the top and between layers.

5-Fifth Step: Layer the casserole Layer one-third of the potato slices in the buttered casserole dish. Add one-third of the ham and onion mixture, one-third of the cheese, and one-third of the cream mixture. Repeat layering two more times, ending with cheese and cream mixture on top. Press down gently so the layers settle and the sauce penetrates the potatoes.

6-Final Step: Bake and serve Cover the dish with foil and bake for 40 minutes. Remove the foil and bake an additional 20 minutes or longer until bubbly and hot and the top is golden. Total bake time is about 1 hour. Let the casserole rest 10 minutes before cutting into squares. Optionally sprinkle with chopped parsley before serving for a fresh pop of color.