Put the chocolate and soya cream in a bowl over a saucepan of simmering water and heat gently until the chocolate has melted.
Remove from the heat, mix in the liqueur and cool the mixture quickly by putting the bowl into a bowl of cold water.
Once the mixture cold and beginning to set, whisk it hard until it is thick and light – using an electric whisk or food processor.
Put the whipped mixture in the fridge to chill until it is solid enough to shape.
Sprinkle a tablespoonful of cocoa onto a plate.
Using two teaspoons, put generous teaspoonfuls of the chocolate mixture on top of the cocoa.
Sift another tablespoonful of cocoa on top, then quickly roll the teaspoonfuls of mixture between your palms to make the truffles.
Put them onto a plate and chill until needed.