I have checked out a couple of receipes for the Milk Sauce. I think it originates in the past, when people were poor and butter was unavailable or expensive. For a 'roux' you need fat, so they used the melted fat from when they fried the preserved pork ( bacon). As a benefit, it tasted nice, maybe nicer than the white sauce made with butter based roux! Oh yes, Russians got loads and loads of Spam. The food ( and industrial) production went sharply down after the Revolution, and even more down once they got involved in WW2. First the know-how got shot as traitors of the proletariat, then the workers got shot either by the German side or by own Kommissars / Politruks. US shipped HUGE amounts of basically everything to them. UK too, despite. Quite a few Hurricanes and Spits are wrecked in Russia. I love the history behind our dishes.