For the espresso truffles, coarsely chop the chocolate coating. Bring whipping cream with sugar and espresso powder to a boil and stir until sugar dissolves.
Remove the saucepan from the heat and add the couverture. Stir until the couverture is completely dissolved and an evenly shiny mass is formed. Refrigerate this for at least 3 hours.
Add the butter to the cold chocolate mixture and beat with a hand mixer until homogeneous.
Using a teaspoon, take an amount of the truffle mixture just about the size of a walnut and shape it into a ball (it is advisable to wear disposable gloves). Roll the truffle in the cocoa powder.
Store the espresso truffles in a cool, dry place.