Covered sweet potatoes and cook for about 20 minutes. In the meantime, peel and finely dice the shallots for the lime dip. Wash the lime hot, dry and finely grate the peel. Halve the lime. Squeeze one half and cut the other half into slices.
Mix sour cream, shallots, lime juice and zest. Season with salt, pepper and 1 pinch of sugar.
Drain, rinse and peel the sweet potatoes. While still hot, press them through a potato press and let them cool down for 5 minutes.
Grate parmesan. Knead 30 g cheese with the sweet potatoes, about 1 teaspoon salt, 250 g flour and egg to a smooth dough (if the mixture is too soft, knead in a spoonful of flour).
Bring plenty of salted water to the boil in a wide saucepan. Use two tablespoons of the potato mixture to form cams, dipping spoons in cold water from time to time. Cook the dumplings at low heat in boiling salted water for 6-8 minutes.
Remove with a skimmer and allow to drip off.
Wash sage, dab dry, chop leaves coarsely. Heat butter in a large pan. Fry the noodles for 2-3 minutes, turning them until golden brown. Fry the sage briefly. Season with salt and pepper.
Serve everything, sprinkle with the rest of the Parmesan cheese.