Wash the lemon hot, grate dry, finely grate the peel and squeeze the juice. Mix sugar with lemon juice and zest. Set aside covered. Remove the crusts from white bread and soak in water.
Meanwhile wash the marjoram, shake dry and chop finely. Peel onion and chop finely. Heat the oil in a pan. Sauté the diced onion in the oil until colourless and remove from the pan. Squeeze the white bread thoroughly. Knead minced meat with onion, marjoram, bread, mustard and paprika. Season well with salt and pepper. Cover and chill.
Cut 4 sausages in half lengthwise and crosswise, so that each sausage has 4 pieces of the same size. Halve the remaining sausages. Cut the ends of the 4 sausage halves approx. 1 cm deep (mouth). Prick 2 holes for the eyes with a wooden skewer and put a peppercorn in each hole.
Form 4 oval meatballs from the minced mass. Place 4 pieces of sausage with the cut surface facing down as legs x-shaped on a baking tray lined with baking paper. Place the meatballs as bodies on top. Put the head parts of sausage into the body of the meatball.
Let the puff pastry thaw and roll out a little thinner on a floured work surface. Cut into approx. 24 narrow strips of approx. 6 cm length. Place 6 lattice-like strips on each meatball and press lightly. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 15-20 minutes. Cover with foil if necessary.
In the meantime, clean, wash and spin-dry the salad and cut into fine strips. Peel, wash and dry grate the potatoes and cut them into narrow slices. Heat the fat in a wide saucepan. Fry the potato wedges in it in portions until crispy, lift them out and let them drip off on kitchen paper. Sprinkle with salt and curry. Remove turtles from the oven, arrange on plates with salad, lemon vinaigrette and sweet potato fries.