# How-To:
01 - Preheat oven to 350°F. Grease a 9x13 inch baking dish with butter or nonstick spray.
02 - In a large saucepan, melt butter over medium heat. Add onion and cook until softened, about 3–4 minutes. Stir in garlic and cook for 1 minute.
03 - Sprinkle in flour and cook, whisking constantly, for 1–2 minutes to form a roux. Gradually whisk in milk and cream, ensuring no lumps form.
04 - Simmer sauce for 3–4 minutes, stirring until thickened. Season with salt, pepper, and nutmeg. Remove from heat and stir in half of the Gruyère and cheddar cheeses until melted.
05 - Arrange half the sliced potatoes in the prepared baking dish. Top with half the ham and pour over half the cheese sauce. Repeat with remaining potatoes, ham, and sauce.
06 - Sprinkle remaining Gruyère, cheddar, and all the Parmesan cheese evenly over the top.
07 - Cover with foil and bake for 45 minutes.
08 - Remove foil and bake for an additional 25–30 minutes, or until potatoes are tender and top is golden brown. Let rest for 10 minutes before serving. Garnish with chopped parsley if desired.
