Chop the ruby chocolate and scrape into a bowl.
In a small saucepan, warm the cream just until hot, and it's beginning to simmer around the edges.
Pour the hot cream over the ruby chocolate, then stir into a smooth ganache.
Cover the ruby chocolate ganache, and refrigerate for at least 8 hours, or overnight, until firm enough to scoop into balls.
Scoop the ruby chocolate into 8 balls, and place on wax paper. Freeze for 1 hour.
Melt the semi-sweet chocolate, either in the microwave at 50% power or over a double boiler, until smooth.
Dip the chilled ruby chocolate balls in the melted chocolate, shake off the excess, and place on the wax paper. Let sit until the chocolate hardens. For the swirl on top, use a spoon to spoon a little more melted chocolate on top of each truffle, then swirl it around.