1. Preheat oven to 350°F. Microwave chocolate and butter in medium microwavable bowl on HIGH 2 minutes or until butter is melted. Stir until chocolate is completely melted. Cool chocolate about 5 minutes or until chocolate is lukewarm to the touch.
2. Beat cake mix, milk, eggs, cinnamon and chocolate mixture in large bowl with electric mixer on low speed just until moistened, scraping side of bowl frequently. Beat on medium speed 2 minutes or until well blended. Pour evenly into 2 greased and floured (9-inch) round cake pans.
3. Bake 25 to 28 minutes or until toothpick inserted in centers comes out clean. Cool cakes in pans 10 minutes. Rmove from pans; cool completely on wire racks.
4. Fill and frost cooled cake with Cinnamon Cream Cheese Frosting.
Tips
Cinnamon Cream Cheese Frosting: Beat 1 package (8 ounces) cream cheese, softened, 1/4 cup (1/2 stick) butter, softened, 1 teaspoon McCormick® Pure Vanilla Extract and 1/2 teaspoon McCormick® Gourmet Collection Saigon Cinnamon in large bowl until well blended. Gradually add 1 package (16 ounces) confectioners' sugar, beating until well blended after each addition.