In a medium mixing bowl, combine the graham cracker crumbs with the melted butter. Mix well until all the crumbs are evenly coated and have a sandy consistency.
Using your fingers or the back of a measuring cup, firmly press the crumb mixture into the bottom and along the sides of a 9-inch pie dish to form an even crust. Once done, place the crust in the refrigerator to chill while you prepare the filling.
In a large mixing bowl, whisk together the sweetened condensed milk, freshly squeezed lemon juice, and lemon zest until the mixture is smooth and well blended.
In a separate bowl, using a hand or stand mixer, whip the heavy cream on medium speed until soft peaks begin to form. Gradually sprinkle in the powdered sugar while continuing to whip, until you achieve stiff peaks that hold their shape.
Carefully fold the whipped cream into the lemon mixture using a spatula.
Pour the luminous lemon filling into your chilled graham cracker crust. Use a spatula to spread the filling evenly across the top.
Cover the pie with plastic wrap and refrigerate for a minimum of 4 hours, or preferably overnight, until the pie is fully set and firm to the touch.
Once set, slice the pie into wedges and serve chilled. For an extra touch of freshness, garnish each slice with a sprig of fresh mint leaves if desired.