Quark is a cultured dairy product that tastes similer to fromage blanc, but some describe it as being more similar to yogurt, either of which would make a good substitute in case you can't find it in your local supermarket or natural foods store. Here it is combined with cream and sweetened condensed milk, plus eggs for added richness. This is not a creamy pudding that's cooked on the stove but instead akin to British puddings that are baked in the oven, for a texture that's like a super moist cake.