I made my cake the night before and I found that the cake absorbed some of the moisture from the sour cream mixture, which made it better! (To be honest, again, that was Arkadi's idea - he said it was so that the flavours will blend better).
Surprisingly, even with a can of sweetened condensed milk, the cake was just lightly sweet. It went real well with tea! Most of all, I got my father in law's approval - even though he too has never heard of "mashenka."