Spray a 13x9 baking pan with non-stick cooking spray or shortening and then coat lightly with flour. Set aside.
Preheat the oven to 350 degrees F.
Melt the white chocolate and allow it to cool while mixing the cake.
In a large bowl, beat together cake mix, egg whites, oil, buttermilk, and peppermint extract until smooth.
Stir in the melted white chocolate until smooth.
Spread the batter evenly into the prepared baking pan.
Bake for 25-30 minutes or until toothpick inserted in the center comes out clean.
Remove and allow the cake to cool to warm temperature.
In a large bowl, whisk together the pudding and milk until it is completely smooth.
Using the handle of a wooden spoon, poke holes into the warm cake.
Slowly pour the pudding mixture into the holes in the cake.
Smooth the remaining pudding mixture on top of the cake.
Cover and place it in the refrigerator for at least 4 hours or overnight to set.
When you are ready to serve, frost with whipped topping and garnish with crushed candy canes.
Serve immediately.
Store any leftovers in the refrigerator.