Place the chocolate on a chopping board and chop into small pieces. Alternatively use chocolate pellets. Place in a heatproof bowl. Add the cream and butter. Place over a pan of hot water and heat gently. Stir until the chocolate and butter melts and combines with the cream to produce a smooth ganache.
Remove from the heat and allow to stand for about 15 minutes to cool slightly. Using a hand held electric whisk, gradually whisk in the prosecco. Continue whisking until the ganache has thickened sufficiently to pipe.
Spoon into a piping bag fitted with a 1cm plain nozzle. Pipe about 40 small, even sized blobs onto a baking tray lined with baking parchment. Chill for 20 minutes or until just firm. The neater the blobs are at this stage the better as there will be less rolling which can be a bit messy.
Lightly dust the chilled ganache with cocoa powder. Then sprinkle a generous layer of cocoa powder onto a small plate. Place a blob of ganache onto the plate and, using your fingers, roll into a ball and return to the baking sheet. Make sure you keep your hands cool. Once you have rolled all the balls chill again for at least 10 minutes .
To coat the truffles, melt about two thirds of the chocolate over a pan of hot water. Remove from the heat. Add the remaining chocolate and stir continuously until all the chocolate has melted.
Dip the fingertips of both hands into the now tempered chocolate and pick up a truffle. Roll the truffle in a circular movement between your fingertips until coated in the chocolate. Place on a clean sheet of baking parchment.
Once all the truffles have been dipped, repeat the rolling again to add a second, slightly thicker, layer of chocolate. Return to the baking parchment and allow to set.
The number of truffles you make will depend on the size you pipe the blobs. They should be about the size of a large cherry. In addition to the preparation time you will need to allow time for cooling and chilling. The truffles can be served immediately or stored in a cool dry place for a up to a week. They are best eaten at room temperature.Nutrition information is approximate and is meant as a guideline only.