Preparation
Stir sugar, star anise, cream of tartar, and 3 tablespoons water in a medium saucepan to blend. Bring to a boil over medium-high heat and cook, swirling occasionally (do not stir), until sugar is caramelized and the color of dark maple syrup, about 8 minutes. Remove from heat and carefully add 1/4 cup red wine (mixture will bubble vigorously), stirring to dissolve. Add remaining 1/4 cup red wine. Boil for 30 seconds, stirring to make sure all sugar is dissolved. Let cool completely. DO AHEAD Red wine caramel can be made 1 week ahead. Cover and chill. Rewarm slightly to loosen before using.