Cook the potatoes with their skins in salted water for 30 minutes.
Cut the yellow peppers and red peppers into 3 cm pieces. Pre-boil in boiling water for 5 minutes, rinse and drain.
Cut the onions into eighths. Fry in oil over medium-high heat until translucent, about 5-7 minutes. Wash and finely chop the fresh herbs.
Whisk the crème fraîche, whipped cream, and egg yolks together. Mix half of the cheese into this mixture.
Preheat the oven to 175°C (347°F).
Drain the potatoes and let cool for 5 minutes. Peel the potatoes and cut into slices.
Grease a baking dish with fat. Layer potatoes in the dish, sprinkle with herbs, and pour some of the cream mixture over it. Spread half of the peppers on top and pour in more cream mixture.
Continue layering with the remaining potatoes and cream mixture. Add the remaining peppers and onions on top. Scatter the remaining cheese over the top.
Bake the casserole in the oven at 175°C (347°F) for 45 minutes until golden.