Be sure to use mini chocolate chips in the cake batter. They will disperse and suspend best; larger chocolate chips will sink to the bottom of the pan. Fine grain caster sugar is recommended for the boiled frosting as it dissolves easily. You can usually find this in the baking aisle at the grocery store, but if you’re coming up empty handed, you can make a close approximation at home. Place regular granulated sugar in a food processor and blend until fine.