Preheat your oven to 350º F.

In a medium bowl, thoroughly whisk all of the filling ingredients together, and set aside to thicken while you prepare the crust.

Blitz the graham crackers in a food processor to fine crumbs. Add the sugar, salt, and cinnamon, and pulse to combine. Finally, add in the butter and pulse until the mixture resembles wet sand.

Press the mixture into a 9-inch pie dish (metal works best, but Pyrex is fine) evenly on the bottom and up the sides.  You want the shallow kind, not the deep-dish. The bottom of a glass or measuring cup can help with pressing it smoothly.

Bake the crust until it is light golden brown and fragrant, 11 to 13 minutes.  Remove from the oven and turn the oven down to 325 F.

Allow the crust to cool for a few minutes, then give you filling a stir and pour it into the crust.

Bake the pie until just set, but slightly wiggly in the center.  This should take 15 to 17 minutes (for me always around 17), and if using the bottled key lime juice it may need more like 20-21 minutes.

Cool the pie to room temperature, then set it in the fridge to chill completely, at least 3 hours or overnight.

Just before serving, you can whip the cream to soft peaks, and spread it on top of the pie.  Personally for me this is gilding the lily.