i’m not sure where my wife picked them up but the sugar granules i used were a lot bigger than typical white sugar and admittedly may not have given them enough time to break down. I haven't used a custard base, but id like to sometime! As for what base I use, it is usually 40% cream, 40% while milk, and 20% sweetener and flavors. I don't stay true to it most of the time just because I like to play around and see what outcomes I get.
brown sugar with corn syrup sound like an interesting combo. i may try that next time