Preheat your oven to 350°F. Lightly grease your tart pan with butter or neutral cooking spray.
In the bowl of a food processor, pulse the graham cracker sheets, in batches if necessary, until you have semi-fine crumbs. You should end up with about 1 1/2 cups of crumbs. Add the coconut flakes, sugar, cinnamon, melted butter, and salt and pulse until the coconut and graham crackers are finely ground and the mixture comes together.
Pour the coconut graham mixture into the tart pan and press the mixture evenly into the bottom and sides of the pan. Bake for about 7-8 minutes or until lightly golden. Let cool to room temperature while you prepare the filling.
Coconut Key Lime Filling
In a medium bowl, whisk the egg yolks until creamy. Add the sweetened condensed milk, coconut cream, key lime juice, and key lime zest until smooth and fully incorporated.
Pour the coconut key lime filling into the cooled pie crust. Bake 10-14 minutes just until the filling is mostly set, but still a little jiggly in the center. Remove the tart from the oven and let it cool for about 30 minutes on a wire rack at room temperature.
Press a piece of plastic wrap to the top of the filling to prevent a skin from forming. Refrigerate the pie until chilled, about 3-4 hours.
Whipped Cream Topping
With a stand mixer or hand mixer, whip the heavy cream, powdered sugar, and vanilla in a medium bowl until stiff peaks form.
Immediately before serving, spread the whipped cream over the top of the pie and garnish with toasted coconut, lime wedges, etc. Slice and serve immediately. Enjoy!
** 8/12/21 Update: An earlier version of this recipe specified using coconut cream instead of coconut milk. I actually tested this recipe later with coconut milk and I didn't notice a texture difference. To use milk instead of cream, just refrigerate a can of coconut milk for about 2-3 hours, and scoop out the thick cream that forms on the top. Avoid the liquid at the bottom of the can, or it could affect the texture.Make sure you're using coconut cream, not cream of coconut used for cocktails. You can find coconut cream in the Thai/Asian aisle of the grocery store.Use fresh (not bottled) lime juice. If you can't find key limes, use regular limes. Occasionally, key limes are also called Mexican limes.If you don't have a food processor to make graham cracker crumbs, simply place the graham crackers in a zipper bag, and use a rolling pin to crush the crackers until fine. Then, mix the crust ingredients by hand.