Defrost the prawns. Wash and peel the asparagus and cut off the woody ends. Cut the asparagus into small pieces. Clean and wash spring onions and cut into fine rings. Cut the prawns roughly into pieces. Wash lemon hot, grate dry. Finely grate half of the peel. Squeeze 1/2 lemon
Heat the oil in a frying pan. Fry the asparagus for 4-5 minutes while turning. Add the prawns and fry for about 1 minute more. Stir in spring onions and lemon peel, season with salt, pepper and lemon juice, fill into a bowl, let cool off
Let the dough sheets rest at room temperature for about 10 minutes. Melt butter. Quarter 1 dough sheet. Lay 1 whole dough sheet flat on the work surface and brush with butter. Place 1 dough sheet on top. Brush 1 quarter of the dough with butter. Place the quarter of dough with the butter facing down in the middle of the 2 dough layers. Add approx. 1/4 of the asparagus mixture. Lift up the ends of the large pastry sheets, fold them into a bag over the filling and tie it up with kitchen twine. Place on a baking tray lined with baking paper. Process the rest of the asparagus mixture, quarters of dough and sheets of dough with a little butter each in the same way. Cover unused pastry sheets with a not too damp cloth. Sprinkle the finished sachets with the remaining liquid butter
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 20-25 minutes on the bottom shelf until brown. In the meantime, wash the chervil and shake dry. Remove the coarse stems from the chervil. Finely chop the remaining chervil. Mix sour cream, quark and chervil, season with salt, pepper and sugar. Take out the sack, arrange
Waiting time approx. 30 minutes