Heat oven to 325°F. Wrap outside bottom and side of 9-inch springform pan with foil to prevent leaking. Lightly spray inside bottom and side of pan with cooking spray. In medium microwavable bowl, melt 16 oz of the chocolate and the butter uncovered on High 1 minute, then in 30-second increments, stirring until smooth. Stir in ground cinnamon and allspice. Cool slightly.