Cold brewed coffee for espresso martinis? Have anybody tried making espresso martinis with cold brewed coffee, or any non-espresso coffee before?

I’d like to start prepping coffee for espresso martinis, we have an espresso machine and while it makes a great espresso it can, at most, do a double shot at a time. Ideally I’d prep 3-4 liters of coffee but that would take a couple of hours on our espresso machine. Thoughts?