“Mokka mit Schlag” is quite correct. The word “Schlag” is an interesting one, perhaps the most lexically complex noun in the German language. Its basic meaning is “blow, stroke”, so in this case it refers to “beaten” cream (i.e. whipped cream). It can also mean worthless merchandise, stuff that looks like it’s been beaten — this sense was imported into English via Yiddish with the spelling “schlock”. Other meanings include “stroke” (in the brain), “bat” (baseball or cricket), “swing” (of a bat), “shock” (electrical), “percussion”, “flop” (theatrical or business), “stamp” (the kind that makes coins), and even “wood-chopping”. It is also the root of a vast number of compounds.