In a bowl, combine the crushed graham crackers with melted butter until the mixture resembles wet sand. Press this mixture firmly into the bottom of a 9x13 inch dish to form an even crust.

In a large mixing bowl, blend the softened cream cheese, sweetened condensed milk, lime juice, lime zest, and vanilla extract using an electric mixer on medium speed until smooth and creamy. This usually takes about 2-3 minutes.

In a separate chilled mixing bowl, pour in the heavy cream and sprinkle in the powdered sugar. Using a hand mixer, whip the mixture on high speed until soft peaks form, which should take about 3-5 minutes.

Gently fold the whipped cream into the cream cheese mixture using a spatula. Be careful not to deflate the whipped cream.

Spoon half of the cheesecake filling over the prepared graham cracker crust, smoothing it out evenly with a spatula. Follow with the remaining cheesecake filling.

Cover the assembled Key Lime Pie Trifle with plastic wrap and refrigerate for at least 2 hours, or until the filling is set.

Top the trifle with fresh whipped cream, and garnish with lime slices and extra zest before serving.