In a medium bowl, mix 1 cup of graham cracker crumbs with 4 tablespoons of melted unsalted butter until evenly coated. Press into the bottom of a trifle dish to form a sturdy base.

Beat 1 cup of heavy whipping cream with an electric mixer until stiff peaks form, approximately 3-5 minutes.

In another bowl, beat 8 ounces of softened cream cheese until smooth. Gradually add 1 cup of powdered sugar, ½ cup of key lime juice, 2 tablespoons of zest, and 1 teaspoon of vanilla extract, mixing well.

Gently fold the whipped cream into the cream cheese filling in two to three additions, preserving the airiness.

Layer half of the lime filling over the graham cracker base, sprinkle with reserved crumbs, then repeat with remaining lime filling.

Cover and refrigerate for at least 2 hours before serving.

Garnish with extra lime zest or whipped cream before serving.