Combine graham cracker crumbs, melted butter, and granulated sugar in a medium bowl, stirring until everything looks like wet sand. Press this mixture firmly into a 9-inch pie pan, covering the bottom and sides evenly. I use the bottom of a measuring cup to get it really compact and flat.

Bake the crust at 350°F for 5 to 7 minutes until it's just set and smells toasty. Don't walk away during this time—mine always bakes faster than I expect. Remove and let it cool completely while you work on the filling.

Whisk together the sweetened condensed milk, fresh key lime juice, key lime zest, vanilla powder, and cornstarch in a large bowl until smooth. The mixture will thicken up slightly as you stir because the cornstarch activates immediately. This is exactly what you want—don't panic if it looks a little thick.

Gently fold in your whipped topping until no white streaks remain, being careful not to deflate all those air bubbles. The filling should look light and fluffy, almost mousse-like. Do this step slowly—rushing it means you'll lose that airy texture.

Pour the filling into your cooled crust and smooth the top with a spatula. Sprinkle the toasted coconut over the top, then refrigerate for at least 4 hours or overnight before slicing. The longer it sits, the more the flavors blend together beautifully.