If you're melting it in the microwave that may be your problem. I can't melt chocolate in the microwave, it will be grainy every time. I use a double boiler, it will melt really smooth but didn't try it with sugar. Maybe melt the chocolate and then add the sugar gradually while stirring until it gets smooth. A little cream might help. When I run upon problems like that I just keep experimenting until I get it right or through it out and forget about itl. LOL I hope you fine something that works for you. T hat's a lot of chocolate.