Start by making the sugar syrup. Put the caster sugar in a small pan over a medium heat and pour in 50ml water. Stir, and bring to the boil.
Turn off the heat and allow the mixture to cool. Put 2 martini glasses in the fridge to chill.
Once the sugar syrup is cold, pour 1 tbsp into a cocktail shaker along with a handful of ice, the vodka, espresso and coffee liqueur. Shake until the outside of the cocktail shaker feels icy cold.
Strain into the chilled glasses. Garnish each one with coffee beans if you like.