Cook the potatoes for what seems like an eternity but is probably somewhere between 25 and 40 minutes in salted, boiling water. Drain, peel and cut into slices.
Heat 3 Tbsp of butter in a frying pan. Add the onions and let them cook 5-6 minutes over low heat.
Add bacon. Cook 2-3 minutes without browning.
Add the potato slices. Cook just until they start to brown.
Mix back in the onions and bacon. Salt and pepper.
Preheat the oven to 425° F (210°C).
Butter a baking dish. Layer it with half the potato-onion-bacon mix and half the slices of Reblochon or shredded cheese. Pour some cream on top. Repeat.
Bake 15 minutes. Serve hot or at whatever temperature it is by the time you've gathered everyone to sit down to eat.
A side salad as accompaniment may ease your conscience.