I do like a good espresso martini, though I’m also a gin martini purist and don’t have more than a handful of uses for vodka.
I’ve always just done 2oz vodka (preferably Reyka), 1oz espresso, and 3/4oz simple or maple syrup. Easy to remember because it’s the same spirit:juice:syrup proportions I use for any and every sour variation.
Edit - shake it with ice like you’re trying to kill it, and if possible and applicable try to work quickly to get it mixed before the espresso shot “dies.” A typical espresso shot will be enough for two drinks so it’s a convenient drink to make for two.
If you don’t have a home espresso rig you could use some of the stronger Aero Press methods, a Moka Pot, or the espresso-like options for the various pod coffee makers. Real espresso is different but I think the cocktail is still pretty forgiving.