Heat oven to 375℉.
Combine graham cracker crumbs, butter, and 3 tablespoons sugar in a medium bowl; mix well.
1 1/2 Cups Graham Cracker Crumbs, 6 Tablespoons Unsalted Butter, melted and cooled, 5 Tablespoons Sugar
Press into a 9-inch pie plate, and bake until lightly browned, about 12
minutes.
Remove from oven, and transfer to a wire rack until completely cooled.
Lower oven to 325℉.
In a medium bowl, gently whisk together condensed milk, egg yolks, key lime juice, and zest.
1/2 Cups Freshly Squeezed Key Lime Juice, 1 Can (14 ounces) Sweetened Condensed Milk
Pour into the prepared, cooled crust.
Return pie to oven, and bake until the center is set but still
quivers when the pan is nudged, about 15 to 17 minutes.
Let cool completely on a wire rack.
Shortly before serving, combine cream and remaining 2 tablespoons sugar in the bowl of an electric mixer fitted with a whisk attachment.
1 Tablespoons Grated Key lime Zest, plus more for garnish
Whisk on medium speed until soft peaks form, 2 to 3 minutes.
Spoon over cooled pie and garnish with zest.
Serve immediately.