Peel the sweet potatoes, cut into halves lengthwise and cut into slices. Finely grind coriander, cumin and pepper in a mortar. Mix with sea salt, turmeric and olive oil. Mix the potato wedges with the spice oil and spread on the fat pan of the oven. Bake in the preheated oven (electric cooker: 200 °C/ circulating air: 175 °C/ gas: see manufacturer) for approx. 40 minutes. Turn once after half the baking time
Meanwhile, wash the lemon hot, grate dry and finely grate the peel. Halve the lemon, squeeze one half. Mix crème fraîche, 2 tablespoons lemon juice and zest, except for a little bit for garnishing. Season to taste with sugar, salt and pepper
Arrange potato wedges on plates. Garnish dip with remaining lemon peel and serve