In a medium bowl, combine graham cracker crumbs with melted unsalted butter until the mixture resembles wet sand. Press firmly into the bottom of a trifle dish to form a solid crust. Cover and refrigerate for about 30 minutes.

In a chilled mixing bowl, pour the heavy whipping cream and beat on medium-high speed until stiff peaks form, about 3-5 minutes. Set aside.

In a large bowl, beat softened cream cheese until smooth. Gradually add powdered sugar, key lime juice, zest, and vanilla extract, mixing until smooth.

Gently fold the whipped cream into the cream cheese-lime mixture using a spatula, ensuring you maintain the airy texture.

Spread half of the lime filling evenly over the chilled crust. Sprinkle a layer of extra graham cracker crumbs, then add the remaining lime filling and top with more crumbs and lime zest.

Cover with plastic wrap and refrigerate for at least 120 minutes, preferably overnight. Serve chilled.