In a medium bowl, combine graham cracker crumbs with melted unsalted butter until evenly coated. Press firmly into the bottom of the serving dish and reserve ½ cup of crumbs.

In a chilled mixing bowl, whip heavy cream on medium speed until stiff peaks form, about 3-5 minutes. Set aside carefully.

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

Gently fold whipped cream into the cream cheese mixture in three stages to maintain airy texture.

Spoon half of creamy filling over the crust in the serving dish, then sprinkle with reserved graham cracker crumbs. Add remaining filling on top.

Top with remaining graham cracker crumbs and lime zest. Cover and chill in refrigerator for at least 2 hours before serving.