The phrase "double latte" refers to a type of coffee beverage that has twice the amount of espresso compared to a regular latte. It is a stronger and more caffeinated drink. Full definition
Ivey noted that even the construction workers in his building were ordering double lattes. (firstthings.com)
When it was his turn with the barrista, (that's the Starbucks term for the counter help, if female) he said, «I'll have a tall double java mocha espresso double latte, please.» (firstthings.com)
For example, last year's Sierra Nevada's Beer Camp variety pack featured joint efforts from a dozen breweries, including Ninkasi's Double Latte Coffee Milk Stout. (bonappetit.com)