Melt it properly
Never melt chocolate in a pan directly over the heat. Either melt it in a bain-marie or large saucepan or in a microwave, stirring regularly. In a bain-marie or large saucepan, put a heat-proof bowl in your pan of hot water and melt the chocolate gently in the bowl, adding a few drops of water. If it's not smooth enough, add a bit of lukewarm water and stir vigorously.
Spread an even layer of melted chocolate out onto a cold surface and leave to cool. Run a grater over the surface of the chocolate to get shavings.
Add a knob of butter to your melted chocolate.