Preheat oven to 350°F with rack in center position
Crush graham crackers in a sealed bag until fine crumbs form
Mix graham cracker crumbs with melted butter, granulated sugar, egg yolk, and salt until mixture resembles wet sand
Press mixture firmly into a 9-inch pie plate, covering bottom and sides evenly
Bake crust for 8-12 minutes until fragrant, firm, and dark brown at edges
Reduce oven temperature to 325°F
Combine lime zest, 5 egg yolks, sweetened condensed milk, lime juice, salt, and vanilla in a bowl and whisk until smooth
Pour filling into cooled crust and smooth the surface
Bake filling for 15-20 minutes until set with slight wobble in center
Cool pie at room temperature for about 1 hour, then refrigerate for at least 2 hours
Mix room temperature cream cheese with powdered sugar until smooth
Slowly whisk in cold heavy cream a little at a time to prevent lumps
Continue whisking until soft to medium peaks form
Spread whipped cream topping over chilled pie nearly to edges
Refrigerate topping for at least 15 minutes until set
Top with fresh lime zest, slice, and serve
