Beat eggs, sugar and salt to an airy light mass.
Add softened butter, quark, lemon zest and vanilla and mix.
Add the pre-dough and mix it.
Add flour in batches and knead it into a very soft, sticky dough. Then knead the dough for about 12 - 15 minutes and let it rise, covered, in a warm place for 1 hour.
Cut soft apricots into small pieces.
Knead the soft apricots and candied orange peel into the dough either with kneading picks or with oiled hands.
Let the dough rise, covered, in a warm place for another 30 minutes.
Line the kulich baking pans completely with baking paper. Alternatively, you can grease the baking pans with butter and dust them with flour, tapping off the excess flour.
Fill the kulich baking pans about 1/3 full with the dough and let them rise in a warm place for 30 minutes.
Bake the kulichi in a preheated oven at 338 °F (170 °C) on the second rack from the bottom for about 40 - 50 minutes, depending on the size of the baking pan. If the surface of the kulichi becomes too brown before they are cooked, cover them with baking paper on top in the oven.
Let the kulichi cool briefly in the baking pans, then carefully take them out, place them on their sides on a kitchen grate and let them cool, turning them over and over during this time.