2 cans (15 ounces) mandarin oranges, divided
1 box (2 layer) devil’s food cake mix
1/2 cup vegetable oil
1 orange, peel grated (optional)
1 package (4-serving size) vanilla flavor instant pudding
2 cups frozen whipped topping, thawed
1 cup heavy whipping cream
1 cup semisweet chocolate
Heat oven to 350 degrees. Spray two (9-inch) cake pans with cooking spray. Drain mandarin oranges, keeping fruit and syrup reserved separately. In large bowl, combine cake mix, juice from one can of mandarin oranges, eggs, oil and orange peel; beat 2 minutes. Pour cake mix into prepared pans. Layer mandarin oranges from one can over each cake and gently submerge them into cake batter. Bake 25-30 minutes or until toothpick inserted in center comes out clean. Cool in pan 10 minutes. Remove from pan onto wire rack; cool completely.
Pour 1/2 cup reserved juice from second can of oranges in bowl with pudding mix; whisk 2 minutes or until pudding mix is completely dissolved. Remove 12 orange slices from second can and dry with paper towel; set aside. Fold in whipped topping and remaining mandarin oranges. Spread mandarin frosting on top of first layer of cake and out to edges. Place second layer on top of first layer.
In small saucepan, heat cream until just beginning to steam, but do not boil. Remove from stove and stir in chocolate. Stir until well-blended. Pour chocolate mixture over cake and garnish with reserved mandarin oranges. Refrigerate 30 minutes before serving.