Chocolate Chile Barbecue Sauce

From: Meathead: The Science of Great Barbecue and Grilling by Meathead Goldwyn with Greg Blonder, PhD, foreword by J. Kenji Lopez-Alt. 

¾ cup sugar
½ cup water
¾ cup rice vinegar
½ cup tomato paste
¼ cup orange juice
2 Tbsp. unsweetened cocoa powder
1 Tbsp. Worcestershire sauce
½ tsp. pure vanilla extract
½ tsp. kosher salt
⅛ tsp. chipotle chile powder

Combine sugar and water in a saucepan and bring to a simmer over low heat. Simmer until the sugar has dissolved, then add remaining ingredients. Stir well. Simmer for a half hour.