• Preheat oven to 325 degrees.

To make the filling:

• In a medium bowl, whisk together egg yolks and lime zest until lightly green, about 2 minutes. 
• Whisk in condensed milk until smooth, then whisk in lime juice. Cover and let sit at room temperature until thickened, about 30 minutes.

To make the crust:

• In a food processor, or in a plastic bag with a rolling pin, finely crush graham crackers.
• In a medium bowl, combine graham cracker crumbs, butter, and sugar. Pour into a 9-inch pie plate, using the bottom of a measuring cup to press the crust evenly and firmly into the bottom and up the sides of the pie plate.
• Bake until golden brown and fragrant, 15 to 20 minutes. Remove from oven and transfer to wire rack (do not turn off oven). 

To assemble the pie:

• Pour thickened filling into warm pie crust. Bake until center is firm but still jiggly when shaken, 15 to 20 minutes. Transfer to wire rack and cool 1 hour.
• Cover pie loosely with plastic wrap and refrigerate until filling is chilled, at least 3 hours or up to 24 hours.

To make the topping:

• In a standing mixer fit with the whisk attachment, or with an electric mixer, whip cream and sugar on medium-low speed until foamy, about 1 minute. 
• Increase speed to high until soft peaks form, about 1 to 3 minutes. Spread whipped cream over the top of pie or pipe a design around the edge. Garnish with lime zest.