Prepare 4 martini glasses by chilling them in the fridge for 30 minutes.
Add the heavy cream to a shaker with 3 ice cubes and shake to lightly whip. In a separate cocktail shaker filled with ice, add the vodka and coffee liqueur. Shake vigorously, then strain into the chilled glasses. Top each with a layer of the cream. Use a rasp grater to grate 1 espresso bean over the top of each cocktail and serve immediately.