Wash and peel the potatoes carefully. Slice them into thin, even rounds using a sharp knife. Keeping slices even helps them cook at the same speed. Place them aside in a bowl.

Preheat your oven to 180°C or 350°F. Lightly grease a baking dish with butter so nothing sticks. This step makes serving easier and helps the potatoes cook evenly in the oven.

Place a saucepan on medium heat and melt the butter. Add flour and stir well to form a smooth base. Cook for one minute, then slowly add milk and cream while stirring constantly.

Add salt, black pepper, and garlic powder into the sauce. Stir gently until everything blends well. Let the sauce cook until it becomes thick, smooth, and rich in texture.

Start layering by placing potatoes in the baking dish. Add some diced ham and sliced onions on top. Pour a portion of sauce over it. Repeat layers until all ingredients are used.

Sprinkle shredded cheddar cheese evenly over the top layer. This will melt during baking and create a golden, slightly crispy topping that adds extra flavor to the dish.

Cover the baking dish with foil and place it in the oven. Bake for 40 minutes, then remove the foil and continue baking for 20 more minutes until golden and bubbling.

Remove the dish from the oven and let it rest for about 10 minutes. This helps the sauce settle and makes slicing and serving much easier while keeping the layers intact.