This is the stuff to spread on the kulich.
Some people put rum or rum essence or brandy in, but I don't like rum and when I first made it the kids were small and wouldn't have appreciated brandy, so the present recipe stuck.
If you don't have a Russian wooden pascha mold (and if you do have a Russian pascha mold, you probably have a Russian pascha recipe too, either handed down from your babushka's babushka or packed with the mold when you got it) you'll need a new conical terracotta flower-pot with a hole in the bottom, as well as either a very old thin linen tea-cloth or a piece of cheesecloth about two feet square. I make a triple batch and use a 20 cm pot; for the amount listed 14 cm is probably enough.
Quark is a white fresh cheese made from whole or skimmed milk. I know that supermarkets in the Netherlands, Belgium, France ("fromage frais entier") and Germany carry it; I don't know about any other countries. Here is the Wikipedia page.
Yes, you do do this in Holy Week. It's the only way to have it ready exactly in time. Pascha doesn't freeze as-is (it does make decent ice cream if you beat in more milk before freezing), and though it keeps for a few weeks in the fridge it's best when eaten at its peak, immediately after turning out.
Put a colander or a large sieve on top of some kind of container. Wet the cheesecloth or tea-towel and line the colander with it. Put the quark in the cloth and turn back the sides of the cloth over it. Put a saucer on top, with something heavy on it (a tin of beans will do), so most of the water drips out of the quark. Leave it for at least 24 hours, ideally 36 hours (set it to drip on Monday afternoon, make the pascha on Wednesday morning).
Heat the cream and butter together until the butter is melted and the mixture very hot; don't let it boil. While it cools to lukewarm, beat the egg yolks with the sugar until the mixture is white and creamy.
Put the egg mixture in a heavy saucepan. Add the cream and butter very gradually, beating all the time. Put the pan on low heat and beat until it thickens.
Take off the heat, add chopped fruit, raisins and almonds. Put the pan in a bowl of ice-cold water and stir until cold. Stir in the drained quark, lemon and vanilla.
Scrub the flower-pot under hot running water, rinse with cold water until the pot is cold, drain, but don't let it get completely dry. Rinse the cheesecloth very well and wring out.
Line the pot with the cloth, smoothing out as many folds as possible. Turn the pascha mixture into the pot, press it into the mold to get out as much air as you can, turn the sides of the cloth over the mixture and cover with a saucer and a weight as before.
Put the pot on a deep saucer or a bowl to catch moisture leaking from the hole. Refrigerate.
Empty the saucer occasionally. Try to resist the temptation to taste. It is Holy Week, after all.
Remove the weight and the saucer, turn the cloth back, put a plate on top of the pot upside-down. Turn over pot and plate in one fell swoop. Remove the pot. Remove the cloth very carefully.
Smooth out wrinkles, if necessary, and decorate with almonds and candied fruit (traditionally with a cross and the letters XB, for Christos Voskrese "Christ is risen".)
Spread pascha on kulich. Eat.