Place the chocolate into a medium-sized, heatproof bowl.
In a small saucepan, heat the cream until it just begins to simmer, and then pour it over the chocolate.
Let it sit a minute or two to allow the chocolate to soften. Then gently stir with a whisk until the chocolate has fully melted and the mixture is smooth.
Then cover and set aside until it is set enough to drizzle over the cake, but isn't too runny.