The espresso martini is the most ordered modern cocktail and the most commonly ruined one. Almost every fault traces to the same three decisions: the coffee, the shake, and the sugar.
The short answer
Use freshly pulled espresso, cooled. Shake hard for a full 15 seconds. Build it 2 oz vodka : 1 oz espresso : 0.5 oz coffee liqueur, with a quarter ounce of simple syrup if your coffee runs bitter. Double strain, let the crema settle, then garnish.
That is most of it. The detail below is why.
Why your foam disappears
The cap on an espresso martini is not egg white and it is not luck. It is the coffee’s own oils, emulsified by force. Three things kill it:
Coffee that is not fresh. Espresso starts losing the oils that make crema within about thirty minutes. Coffee brewed an hour ago will produce a thin, grey head at best. This is the single most common cause.
A gentle shake. This drink needs more force than almost anything else on a back bar — a genuinely hard 15 seconds. Most people shake for eight and wonder why.
Hot espresso. Pouring a hot shot into a shaker melts the ice immediately, which over-dilutes the drink and leaves it warm and flat. Let it cool first.
Cold brew instead?
It works, and it will never foam as well. Cold brew is lower in the oils that build the cap. If it is what you have, shake longer and add a quarter ounce of syrup to compensate for the flatter flavour — cold brew is smoother but less aromatic.
Instant coffee will taste like instant coffee. A heaped teaspoon in an ounce of hot water, cooled completely, is the best you will get.
The sugar question
Bradsell’s original used sugar syrup alongside the coffee liqueur. Modern palates often want less. The honest answer is that it depends on your coffee: a bright, acidic espresso needs a little sugar to round it; a dark, chocolatey roast usually does not.
Start at a quarter ounce, taste before you strain, and adjust. The drink should taste of coffee, not of sweetness.
Which coffee liqueur
This is doing real work — it brings body and sweetness the espresso cannot. A thin, oversweet liqueur makes a thin, oversweet drink. Look for something that tastes of coffee rather than of caramel.
And keep it: dropping the liqueur and adding more syrup makes a noticeably worse drink. The two coffee sources are not redundant.
Making it for a group
Partly possible. Pre-mix the vodka, liqueur and syrup and refrigerate — that part holds for days. The espresso has to be fresh and the shake has to happen to order, because the foam cannot be made in advance and will not survive being poured from a jug.
The full build with measurements is on the Espresso Martini recipe page, including its sourced origin and the common mistakes in short form.