In a medium bowl, combine graham cracker crumbs with melted unsalted butter. Press firmly into the bottom of a trifle dish.

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

In a separate bowl, beat softened cream cheese until smooth. Gradually mix in powdered sugar, key lime juice, zest, and vanilla extract until creamy.

Gently fold the whipped cream into the cream cheese mixture in two additions to keep it fluffy.

Spread half of the filling over the crust, sprinkle with graham cracker crumbs, then repeat with remaining filling and crumbs.

Cover with plastic wrap and refrigerate for at least 2 hours to set the layers.