Mix 3 litres of water, vinegar and flour in a wide pot. Wash and peel the black salsifies thoroughly, cut off the ends and put them immediately into the vinegar water. Lift the black salsifies out of the vinegar water and place them in boiling salted water.
Cook for 10-12 minutes.
In the meantime cut the bacon into fine cubes. Heat oil in a pan. Leave the bacon in it while turning it until crispy. Drain on kitchen paper. Wash parsley, shake dry and chop finely, except for a few leaves for garnishing.
Set aside a few bacon cubes for garnishing. Mix chopped parsley, bacon cubes, curd, milk and egg yolks, season with salt, pepper and nutmeg. Lift the black salsify out of the water and drain well on kitchen paper.
Let the dough sheets rest at room temperature for about 10 minutes. Remove 5 dough-sheets from the packaging, pack the rest well and use them for other purposes. Melt butter in a small pot. Grease an ovenproof casserole dish (20 x 30 cm, 3.5 cm deep) with a little butter.
Unroll the dough sheets, brush individual sheets with the liquid butter and place them offset in the mould, pressing slightly so that the edges protrude only slightly.
Cut the black salsifies to just under 20 cm length. Sprinkle filo pastry with breadcrumbs. Place the black salsifies and black salsify sections in the mould to match. Pour the whisked egg and quark mixture over it.
Bake on the lower shelf in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 30 minutes. Cover the edges of the dough with foil after about 20 minutes.
In the meantime, chop the nuts coarsely and roast them in a pan without fat until golden brown. Let them cool down on a flat plate. Remove the tart from the oven. Sprinkle with walnut kernels, remaining bacon and parsley.