Start by preheating your oven to 350°F (175°C). Gather all your ingredients and prepare your pie pan by lightly greasing it or lining it with parchment paper.

In a medium bowl, combine the graham cracker crumbs, sugar, and melted butter. Mix until the ingredients are well combined, resembling wet sand. Press this mixture firmly into the bottom and up the sides of your prepared pie pan to form a crust.

In a separate large bowl, whisk together the sweetened condensed milk, sour cream, key lime juice, and lime zest until smooth. Ensure no lumps remain.

Once your filling is smooth, pour it directly into your prepared crust. Spread it evenly and ensure it fills all corners. Bake in the preheated oven for 10 minutes.

Remove the pie from the oven and let it cool at room temperature.

After cooling, cover the pie with plastic wrap and place it in the refrigerator for at least 3 hours to fully set and develop its flavors.

When ready to serve, remove the pie from the refrigerator, top generously with whipped cream, slice it up, and enjoy!