Step 1

make the crust preheat oven to using a food processor, crush the graham crackers into crumbs.  melt the butter and add it to the graham cracker crumbs along with the sugar and cinnamon.   press crumbly mixture into 9 inch pie plate.  bake at 375 for 7 minutes.  do not overtake, or the crust will be too hard to slice.  cool at room temperature before filling

Step 2

make the filling: combine the sweetened condensed milk, key lime juice, egg, and sour cream.  make sure to blend well using a whisk until there are no bits of egg yolk visible.  pour filling into a bowl, cover, and chill in fridge while the crust cools.

Step 3

assemble and bake Preheat the oven to Pour the lime filling into the graham cracker crust and smooth with a wooden spoon or spatula.  Bake for 10 minutes, until filling is set.. Cool at room temperature then refrigerate at least 3 hours.

Step 4

Make the whipped topping. In the bowl of an electric mixer fitted with the whisk beaters, combine the heavy cream, sugar, vanilla and cream of tartar.  Beat at high for 1-3 minutes until whipped.  Top pie with whipped cream topping by either spreading out gently with a spatula or piping on top. serve cold.