In a medium saucepan, heat sugar, ½ cup (120 grams) cold water, cream, and cocoa over medium-low heat. Simmer until mixture slightly thickens, about 20 minutes.

Place remaining 1 tablespoon (15 grams) cold water in a small bowl. Sprinkle gelatin over top, and let stand until softened, about 5 minutes. Remove chocolate mixture from heat, and whisk in gelatin mixture until combined. Set over an ice bath, and whisk until glaze thickens, about 1 minute.