An espresso drink that is a long black with a dash of milk is commonly known as short macchiato.
When you're wanting a long black with a dash of milk from a coffee shop you should ask for a "short macchiato" which is what it's universally known as.
The word macchiato translates to “stain” or “spot” in Italian speak.
So just ask for a short macchiato and that's what gets me the drink that you're asking about.
I've also heard some places refer to it as a coffee 1 cream in some parts but I would try asking for the short macchiato first.