Step 1: Soak the chopped prunes in port for several hours.
Step 2: Preheat the oven to 220°C. Roast the walnuts on a baking tray for 6–8 minutes, then rub off the skins with a clean tea towel and coarsely chop the nuts.
Step 3: Heat the chocolate gently with the cream in the top of a double saucepan over boiling water. (If you don’t have a double boiler, use a heatproof bowl that fits snugly over a pan of boiling water.) Remove from the heat before all the chocolate has melted. Stir continuously off the heat to finish melting the chocolate, then cool.
Step 4: Fold the drained soaked prunes and chopped nuts into the cooled chocolate mixture, then roll into balls and dust with cocoa.
Maggie's Tip: The prunes can be replaced with the same quantity of diced quince paste; in that case, soak in Cointreau rather than port. The chocolate mixture must be cool before the quince paste is added, otherwise the paste will melt.