In a medium bowl, combine graham cracker crumbs with melted unsalted butter until moistened. Reserve ½ cup of this mixture for later.

Firmly press the prepared graham cracker mixture into the bottom of a trifle dish to create a compact crust.

In a chilled mixing bowl, whip heavy whipping cream on high speed until stiff peaks form, about 3 to 5 minutes.

In another bowl, beat softened cream cheese until smooth. Gradually add powdered sugar, key lime juice, zest, and vanilla; mix until smooth.

Gently fold the whipped cream into the cream cheese mixture in two to three additions.

Spread half of the filling over the crust, then sprinkle one-quarter of the reserved crumb mixture on top.

Add the remaining lime filling, smoothing it out, and finish with the rest of the graham cracker crumbs.

Cover with plastic wrap and refrigerate for at least 2 hours before serving to allow flavors to meld.