Preheat your oven to 425 degrees Fahrenheit. Spray an eight by eight inch baking dish (or a 2 quart baking dish) with cooking spray.
After peeling and slicing your potatoes put them in a large bowl and cover with chicken broth and heavy cream so they don't brown as you prepare the rest of the recipe.
2 1/2 pounds russet potatoes, 1 cup chicken broth, 1 cup heavy cream
Over medium heat in a large Dutch oven, melt the butter. Add in the onion and cook until translucent, five to seven minutes. Add in the garlic powder, salt, thyme, and black pepper.
2 tablespoons unsalted butter, 1 onion, 1 teaspoon garlic powder, 1 teaspoon salt, 1 teaspoon dried thyme, 1/4 teaspoon black pepper
Add the potatoes, cream, and broth to the Dutch oven and bring to a simmer. Cover and cook for 10 minutes or until the potatoes are tender and can be sliced with a paring knife with little resistance. Stir in the ham and one cup of the cheddar cheese.
2 cups cooked ham
Transfer the potato mixture to the baking dish and smooth into an even layer. Top with the remaining cheddar cheese and bake for 10 to 15 minutes.
Let stand 10 minutes. Garnish with fresh parsley and serve.