Place two tall milkshake glasses in the freezer to chill while making the shakes.
Place ice cream, cold coffee, milk, and chocolate syrup in the bowl of a blender.
Pulse to blend together ice cream. Add up to ¼ cup additional milk as needed to thin the shake.
Divide Jamocha shake evenly into two glasses.
Top with whipped cream and additional chocolate syrup, if desired.
Serve immediately.
