This dark sauce takes advantage of chocolate's affinity for red wine. Dutch process cocoa lends the sauce richer chocolate flavor than regular unsweetened cocoa. Store in the refrigerator for up to one week.
Combine first 3 ingredients in a small saucepan; bring to a simmer. Cook 5 minutes. Discard sachet. Add cocoa and corn syrup, stirring with a whisk until smooth. Simmer 2 minutes; remove from heat. Add chocolate, stirring until chocolate melts. Cool to room temperature.