1. To prepare filling, combine first 4 ingredients in a large saucepan; stir until cornstarch dissolves. Heat pan over medium-high heat; bring to a boil, stirring constantly. Cook 1 minute or until sugar mixture is very thick, stirring constantly. Remove sugar mixture from heat. Stir in cherries. Cool completely; cover and set aside.
2. To prepare cake, preheat the oven to 350°.
3. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients (through salt) in a large bowl; stir with a whisk. Combine buttermilk, milk, oil, vanilla, and eggs in a bowl; stir with a whisk. Add buttermilk mixture to sugar mixture; beat with a mixer at medium speed just until well blended (batter will be thin).
4. Pour batter into 2 (9-inch) round cake pans coated with cooking spray. Bake at 350° for 40 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes; remove from pans. Cool completely on wire rack.
5. Place 1 cake layer on a plate, and spoon half of cherry mixture (about 1 1/2 cups) evenly over the top, leaving a 1/4-inch border around edges. Combine whipped topping and kirsch in a small bowl. Spoon 1 cup whipped topping mixture evenly over cherry mixture. Top with remaining cake layer. Spoon remaining 1 1/2 cups cherry mixture onto cake layer, leaving a 1/2-inch border around edges. Spoon remaining 1 cup whipped topping mixture onto cherry mixture, leaving a 2-inch border from the edge of the cake layer. Garnish with chocolate curls. Cover loosely, and chill until ready to serve.