In a large mixing bowl, whip the heavy cream until soft peaks form. Gradually add the powdered sugar and vanilla extract, continuing to whip until stiff peaks form.
In another bowl, combine the sweetened condensed milk and shredded coconut, mixing well.
Gently fold the coconut mixture into the whipped cream until fully combined.
In a 9x13 inch baking dish, layer graham crackers on the bottom. Spread half of the coconut cream mixture over the crackers.
Add another layer of graham crackers, followed by the remaining coconut cream mixture. Top with a final layer of graham crackers.
Cover the dish with plastic wrap and refrigerate for at least 4 hours, or overnight for best results.
Before serving, sprinkle the toasted coconut flakes on top for garnish.