In a large mixing bowl, beat together the heavy cream, powdered sugar, and vanilla until medium peaks form, about 3 to 5 minutes.
Place the mandarin orange slices on a cutting board and rough chop them into small pieces.
Layer two paper towels on top of each other and place the oranges on top. Wrap up the orange pieces and gently press to soak up any extra juice into the paper towels.
Add the orange pieces to the whipped cream, and gently fold the oranges into the whipped cream.
Using a 9-inch by 9-inch baking dish, create a layer of vanilla wafers in the bottom of the dish. (I was able to fit 16 cookies per layer) Place 1/4 of the whipped cream on top of the cookies and use the back of a spoon of a rubber spatula to spread the whipped cream into an even layer.
Repeat the cookie and whipped cream layering three more times, ending with whipped cream on top.
Cut a slit in the orange slice and twist it once. place the twisted orange in the center of the dessert. Sprinkle the orange zest all over the top of the whipped cream. (You could also reserve 4 mandarin oranges and place them in the center of the whipped cream in a starburst.)
Cover the dish with plastic wrap and refrigerate for at least 4 hours. Keep refrigerated until ready to serve.
Cut the icebox cake into the desired number of servings. For large portions, cut the cake into quarters. I cut mine into 9 portions and it was perfect for little after dinner treat.
If you prefer, you can substitute 1 tub of thawed Cool Whip (about 3 cups) for the whipped cream. You can also substitute graham crackers for the vanilla wafers. Break the graham cracker sheets to fit your baking dish, and prepare as directed.