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1 cup light or dark brown sugar
2 tablespoons water
6 tablespoon butter
1/2 teaspoon salt
1/2 teaspoon cider vinegar
3/4 cup heavy cream, divided
1/2 teaspoon rum extract
Four 12-ounce bottles cream soda

In a small saucepan over medium, combine the brown sugar and water. Bring to a gentle boil…