Preheat the oven to 375°F (190ºC). Butter a 10-inch aluminum pie pan. In a food processor combine the graham crackers, sugar, cinnamon and melted butter, pulsing until the graham cracker crumbs are moist.
Pour into the pie pan and press the crumbs evenly along the bottom of the pan and up the sides. Bake the pie crust for 15 minutes or until the crust is lightly browned. Remove from the oven and let cool.
For the filling:
While the pie crust bakes, whisk the key lime zest, lime juice, key lime juice, condensed milk, and eggs together in a large bowl.
Pour the filling into the cooled, prepared pie crust and return to the oven. Bake for 20 minutes, until the filling is set but still jiggles in the middle. Remove the pie from the oven and let cool completely. When the pan is cooled, refrigerate for 6 hours.
For the whipped cream:
When ready to serve, prepare the whipped cream. In a stand-mixer or using a handheld mixer, whisk the heavy cream, sour cream and sugar together until the whipped cream forms stiff peaks.
Spoon the whipped cream into a pastry bag fitted with a large star shape tip.
Hold the pastry bag 1/2” over the pie then decorate the outer edges of the pie with the whipped cream. Sprinkle the pie with the remaining key lime zest and key lime slices for garnish. Serve cold.