Drizzle olive oil on the bottom of the baking dish. Arrange pre-cooked potatoes, sliced into rounds, in a single layer on the bottom of the dish. Season with salt, pepper, and spices. Pour in enough milk to just cover the potatoes.

Add sliced onions. Place strips of ham lengthwise over the potatoes and onions, and sprinkle with a little shredded Gruyère cheese. Then cover everything with slices of raclette cheese. Drizzle a little more olive oil and add more spices on top.

Bake in a preheated oven at 428°F (220°C) for 30 to 35 minutes. Remove from the oven and serve hot.