In a medium bowl, combine the graham cracker crumbs and one-half cup of sugar, pour the melted unsalted butter directly over the top, and stir firmly until the crumbs are uniformly moistened. Set aside exactly 1 cup of these buttery crumbs to use for the final topping, and press the remaining crumbs firmly into an even layer across the bottom of a 9×13-inch baking dish to form the crust.

Pour the lemon gelatin powder into a medium heat-proof bowl, add the 1 cup of boiling hot water, and whisk aggressively for 1 to 2 minutes until every single sugar and gelatin crystal is fully dissolved, then set it aside on the counter to cool until it drops to room temperature but remains completely liquid.

In a separate large bowl, combine the room-temperature cream cheese, one cup of sugar, and the lemon juice, beating with an electric hand mixer on medium speed for 3 to 4 minutes until the mixture transforms into a light, completely smooth, and lump-free paste. Slowly stream the cooled, liquid lemon gelatin into the cream cheese base while mixing on low speed until fully incorporated.

Pull your mixing beaters, a clean glass bowl, and the can of evaporated milk straight out of the freezer where they have been chilling. Pour the icy evaporated milk into the cold bowl and whip on high speed for 4 to 5 minutes until it expands dramatically into dense, thick, and fluffy stiff peaks that mimic whipped cream.

Tip the lemony cream cheese mixture directly into the bowl of whipped evaporated milk, and use a wide rubber spatula to gently fold the two matrices together from the bottom up. Work slowly and treat the mixture kindly to preserve the whipped air pockets, stopping the moment the filling is completely uniform.

Pour the light, aerated cheesecake filling evenly over the graham cracker crust in your baking dish, smoothing the top surface with an offset spatula. Blanket the top uniformly with the 1 cup of reserved buttery graham cracker crumbs, cover tightly with plastic wrap, and refrigerate for a minimum of 4 hours or overnight to let the gelatin network lock the foam into a sliceable icebox dessert.