Russian Christmas
We are attending a Russian Christmas Party on Jan 2, and we are bringing the mushroom soup with zaprashka. I've made mushroom soup before without the zaprashka, which I think is just a butter/flour roux. Does anyone have an authentic recipe for this traditional Russian Christmas dish?

What this tells me, is that I don't get on SE enough because I didn't read a number of interesting looking threads. And I never heard of the cheese sandwich thing. So I'm favorite-ing this in order to catch up over the next few weeks as time allows. Thanks!