Chocolate truffles

1. Warm a mixing bowl to 37-40C/99-104F (it should feel warm but not hot to the touch). Add the chopped chocolate and set aside.
2. In a pan, gently heat the whipping cream until just boiling, then immediately drizzle a quarter of the heated cream into the centre of the chopped chocolate.
3. Stir the cream and chocolate in a single direction, keeping the spoon at the centre of the mixture, until the chocolate pieces have melted and the mixture is smooth and well combined.
4. Drizzle in the remaining cream a little at a time, stirring the mixture in the same direction, then gradually working the spoon to the edges of the mixture until well combined.
5. Set the mixture aside until its temperature is 37C/99F. Add the butter pieces one at a time and stir until the mixture has the consistency of mayonnaise. (NB: You may not need all the butter.)
6. Set the mixture aside in a cool place, overnight if possible. It should cool to 15C/59F (test this with a cooking thermometer).
7. When the truffle mixture has cooled, use a teaspoon to scoop up portions of the truffle mixture. Then, using cool hands, shape each portion into a small ball to form 20 truffles.
8. Dredge the truffles in cocoa powder until completely covered, then serve.
(NB: The truffles will keep for two days. If you want to preserve them for longer, dip the truffles into melted chocolate and set aside to cool before dredging them in the cocoa powder.)