Can I make this without an espresso machine?
Yes. Use strong cold brew concentrate (the real concentrate, not ready-to-drink) or very strong brewed coffee. Start with 1 to 1 1/2 oz per drink and adjust to taste. You will still get great flavor, but espresso is the easiest path to that classic foam cap.
Why do some espresso martinis have no foam?
Usually one of these: the espresso was old or went flat, you used brewed coffee (less natural foam than espresso), there was not enough ice, or the shake was too gentle. For best results, use fresh espresso with a little crema, let it cool until it is no longer steaming, fill the shaker with ice, and shake hard for 15 to 20 seconds.
Do I have to add simple syrup?
No. Coffee liqueur already brings sweetness. Start without it, taste, then add 1 tsp to 1/2 oz (15 ml) if you want it more dessert-like.
What coffee liqueur should I use?
Use what you like, but know they vary a lot in sweetness. Kahlua is sweeter and softer, while something like Mr Black is more coffee-forward and less sweet. If you switch liqueurs, adjust the simple syrup to match your vibe.
What vodka is best?
A clean, mid-range vodka is perfect. You do not need a unicorn bottle. Avoid heavily flavored vodkas unless that is the whole vibe.
Can I make it less boozy?
Yep. Reduce the vodka to 1 1/2 oz and keep the espresso at 1 oz. You will still get bold coffee flavor with a softer punch.
How do I get that super-smooth top?
Double strain through a fine mesh strainer. It keeps ice shards out and gives you a cleaner, tighter-looking foam on top.