Wash the potatoes and beetroot thoroughly. Cut off the beetroot cabbage and roots. Separate the eggs for the salt crust. Beat the egg white with the whisk of the hand mixer until stiff. Mix sea salt, egg yolks, beaten egg white, flour and starch.
On a baking tray lined with baking paper, press one layer of salt dough (approx. 1 cm thick) next to each other in the size of the potatoes and the beetroot. Place the potatoes and beetroot on top and gradually cover with salt dough of equal thickness.
Press firmly again and again. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 45 minutes. For the sour cream, wash the lime hot, rub dry and grate the peel.
Wash the parsley, shake dry, pluck the leaves from the stalks and chop finely, except for something to garnish. Mix quark, sour cream, vinegar, milk, lime zest and parsley. Season to taste with salt, pepper and sugar.
Open salt crusts. Remove potatoes and beetroot. Slice potatoes and peel beetroot and cut into slices. Arrange potatoes with sour cream and beetroot on plates and garnish with parsley.