Prepare the Crust: In a medium bowl, combine the graham cracker crumbs, melted butter, and 1/4 cup of granulated sugar until thoroughly mixed and the texture resembles wet sand.

Press the crust mixture evenly into the bottom of a 9x13 inch baking pan lined with parchment paper, ensuring the edges are compact. Place the pan in the freezer while preparing the filling.

Prepare the Filling Base: In a large, chilled bowl, whip the cold heavy whipping cream until stiff peaks form. Set aside.

Combine Buttermilk Mixture: In a separate bowl, whisk together the cold buttermilk, sifted powdered sugar, vanilla extract, and a dash of salt until the sugar is fully dissolved and the mixture is smooth.

Fold Together: Gently fold the buttermilk mixture into the whipped cream in two additions, being careful not to deflate the volume. The resulting mixture should be light and airy.

Assemble and Freeze: Pour the buttermilk filling evenly over the chilled graham cracker crust. Smooth the top with a spatula.

Freeze for a minimum of 6 hours, or preferably overnight, until completely firm. Cut into squares or slices before serving immediately.