Peel and wash the potatoes, slice or slice them thinly. Peel onions and slice or cut into thin rings. Wash thyme, dab dry, remove leaves.
Heat the oil in a pan. Sauté the onions for 2-3 minutes, do not brown. Sprinkle with 2 tablespoons of sugar and caramelise slightly while stirring. Deglaze with vinegar, bring to the boil and simmer for 2-3 minutes.
Stir in the thyme. Season with salt and pepper.
Preheat oven (electric cooker: 225°C/ circulating air: 200°C/ gas: level 4). Season crème fraîche with salt and pepper. Remove the dough from the packaging and roll out directly on a baking tray with the baking paper.
Spread with crème fraîche. First put the potatoes on top, then the onions. Bake in the oven for about 15 minutes.