It is buckwheat, known to Russians as “Grechka”. It is quite nice, goes well with meat or even mixed with milk.
The white substance is most likely fat.
Haha I forgot we called it grechka. Technically grechnevaya kasha, but colloquially called either grechka or kasha; my grandpa was obsessed with it lol, so we just always called it “ne vkusnaya kasha” aka “not tasty porridge” lol