Start the oven at 200 degree Celsius
Cook the potatoes and then cut them into thin slices.
Peel the onion and cut it into thin slices.
Open the box of bacon and cut it in small pieces.
Spread half of the potatoes in an oven form, sprinkle half of the bacon and half of the onion on top of the potatoes. Add another layer in the same way.
Cut the cheese in half horizontally, and place them (crust side up) on top of the potatoes.
Put the tartiflette in the middle of the oven for 20-30 minutes.
Take out the form from the oven and serve the dish warm.