The preferred way to melt chocolate is in the top pan of a double boiler set over but not touching barely simmering water. As soon as the water simmers, it produces steam, the nemesis of melting chocolate. If even a droplet of moisture gets into the chocolate, it can seize or stiffen. If this happens, start over with new chocolate. Mixing the melted chocolate with vegetable oil causes the formation of small slivers of chocolate in the finished ice cream. This method, perfected by noted cookbook author Nick Malgieri, yields a distinctive and well-blended ice cream.