Add NILLA Wafers and sugar to the bowl of a food processor and pulse until fine crumbs form. Transfer to a medium bowl and add coconut flakes and melted butter. Toss to combine completely. Pour the crumbs into a 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.
For The Filling
In a large bowl, combine the sweetened condensed milk and lime juice. Stir until thick and well incorporated. Set aside.
Place the gelatin in a small bowl and cover with water. 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 -- very important.
Add the whipping cream to the bowl of a stand mixer (if you don't have a stand mixer use a large mixing bowl and a handheld mixer) Whip the cream for one minute on a medium speed. Slowly add the sugar 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 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, careful not to deflate the cream too much.
Pour the filling into the cooled pie crust and smooth over with a spatula.
For The Topping
Add reserved whipped cream 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 and slices of key lime. 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.
If you don't want to freeze the tart, just refrigerate it, it will be more mousse-like than firm and just as delicious. Because we've stabilized the whipped cream, the tart will last in the refrigerator for up to 2-3 days.