In a mixing bowl, combine the graham cracker crumbs and granulated sugar. Drizzle in the melted butter while stirring until the crumbs are evenly coated. The mixture should hold together when pressed. Set aside.

In another bowl, beat the softened cream cheese until smooth. Gradually add the sweetened condensed milk, mixing until creamy. Next, add the key lime juice and lime zest, blending until everything is well combined and silky.

In a third bowl, whip the heavy cream using an electric mixer until soft peaks form. Gradually add in powdered sugar and vanilla extract, continuing to whip until stiff peaks form. This should take about 3-5 minutes.

In a trifle dish or individual glasses, layer one-third of the graham cracker mixture, followed by half of the filling, and then a layer of whipped cream. Repeat the layers, finishing with whipped cream and topping it off with a sprinkle of lime zest.

Cover and chill in the refrigerator for at least 2 hours before serving. This allows the flavors to meld perfectly together.