Preheat oven to 350 degrees F (180 degrees C).
Add Nilla Wafers (2 cup) and Granulated Sugar (1/4 cup) to the bowl of a food processor and pulse until fine crumbs form. Transfer to a medium bowl and add Sweetened Coconut Flakes (1/2 cup), and Butter (5 tablespoon). Toss to combine completely.
Pour the crumbs into an 8" tart pan with removable bottom. Press the crumbs into the bottom and sides of the pan. Bake for 8-10 minutes or until browned. Set aside to cool completely.
In a large bowl, combine the Sweetened Condensed Milk (15 ounce) and Key Lime Juice (1/2 cup). Stir until thick and well incorporated. Set aside.
Place the Gelatin Powder (2 teaspoon) in a small bowl and cover with Water (2 tablespoon). Let stand two minutes to bloom. Microwave in 10-second bursts until gelatin is dissolved. Cool the gelatin to near room temperature, but do not let it set.
Add the Heavy Cream (2 cup) to the bowl of a stand mixer. Whip the cream for one minute at medium speed.
Slowly add the Granulated Sugar (5 tablespoon) to the cream. Turn off the mixer and check to see that the gelatin has cooled, but not set.
Add the gelatin and continue to whip until stiff peaks form. Separately reserve about 1 - 1 1/2 cups of whipped topping for garnish.
Spoon about 1/2 cup of the whipped cream into the key lime filling and lightly stir to combine. Add the rest of the whipped cream and fold completely into the mixture.
Pour the filling into the cooled pie crust and smooth over with a spatula.
Add reserved Whipped Cream (1 cup) to a piping bag fitted with a large star tip. Fold the end of the bag over once or twice to seal and use a steady pressure to pipe the whipped cream around the edge of the tart and in the center.
Sprinkle with Toasted Coconut Flakes (1/2 cup) and Lime (1). Refrigerate for at least two hours for a cloud-like dessert. For a frozen tart -- freeze at least two hours. To serve, remove the tart from the freezer and let it sit out on the counter for 10-15 minutes to soften a little before slicing it.