Chill four martini glasses. Combine the espresso, vodka, simple syrup, and amaretto in a martini shaker. Fill the shaker with ice. Shake for about 10 seconds. Divide between the chilled martini glasses. Serve immediately.
Simple Syrup: In a saucepan combine water and sugar over medium heat. Bring to a boil, reduce heat and simmer for 5 minutes, until the sugar has dissolved. Take the pan off the heat and cool the syrup. Any extra cooled syrup can be saved in an airtight container in the refrigerator. Makes 240ml. Prep Time: 5 minutes Cook Time: 5 minutes