In a food processor, pulse the graham crackers to a fine crumb. Add the sugar, melted butter, and cinnamon and pulse until the mixture is well blended. Press the graham cracker mixture into a 9-inch pie plate.
Bake the crust for 8-10 minutes, until lightly golden brown. Set aside to cool.
In a medium bowl, whisk together the condensed milk, key lime juice, and lime zest until smooth. Pour into the cooled graham cracker crust.
Bake for about 15 minutes, until the filling is set. Cool to room temperature, then chill in the refrigerator for at least 2 hours before serving.
Garnish with whipped cream, if desired.
Interesting Facts
Key lime pie is a classic American dessert that is believed to have originated in the Florida Keys.
The graham cracker crust is a common variation on the traditional pastry crust.
Key lime juice has a distinct tartness and can be found in most grocery stores.