Peel and finely dice the onions and garlic. Clean and clean the mushrooms and cut them into small cubes
Heat 2 tablespoons of oil and 1 tablespoon of butter in 2 large, coated pans. Add onions and garlic in equal parts to the pans and sauté over low heat for about 5 minutes, stirring continuously. Divide the mushrooms between both pans and fry them while stirring until there is no liquid in the pans. Put the mushrooms in a sieve and let them cool down
Take the strudel dough out of the refrigerator and let it rest at room temperature for about 10 minutes. In the meantime, finely chop the hazelnut kernels and roast them lightly in a pan without fat, remove. Roast ground hazelnuts as well. Wash parsley, dab dry, remove leaves and cut finely. Put mushrooms, parsley and chopped nuts into a bowl, mix in sour cream and mustard and season with salt, pepper, lemon juice and sugar.
Melt 125 g butter. Moisten 2 tea towels and lay them next to each other with a slight overlap. Place 2 more dry dish towels on top of each other. Place 3 strudel dough sheets on the dish towels, slightly overlapping, and brush with butter. Place another 2 times 3 more strudel sheets on top of each other and brush with butter. Place the last sheet in the middle. Sprinkle with ground hazelnuts. Place the mushrooms as a skein on one long side, leaving a 3 cm wide edge free at the bottom. Turn over the sides, carefully roll up from the long side using the cloths. Brush the roll with butter, form it into a snail and place it on a baking tray lined with baking paper. Sprinkle with sesame seeds and bake in a preheated oven (electric range: 200 °C/ convection oven: 175 °C/ gas: level 3) for 35-40 minutes
Waiting time approx. 1 hour