2 Split the piece of leek lengthwise, rinse thoroughly under running water, drain and cut into thin half-moons.
3 Heat oil in a pot and cook the vegetables for about 3 minutes. Pour in 600 ml (approximately 2 1/2 cups) of water, add salt and cover; cook for about 15 minutes over medium heat.
4 Meanwhile, mix quark with egg in a bowl, add semolina and grated Parmesan and stir. Season with salt and freshly grated nutmeg.
5 Divide semolina mixture into 2 portions and place in separate bowls. Mix tomato paste into one portion.
6 Rinse basil, shake dry, pluck leaves and finely chop. Mix with the other portion of semolina mixture.
7 Submerge 2 tablespoons in water and then use them to scoop about 4 oval shapes (quenelles) from each of the two semolina portions. Add to the soup, cover and let simmer on low heat until dumplings rise to the top, about 5 minutes. Serve immediately.