Preheat your oven to 350°F (175°C). In a medium bowl, combine the graham cracker crumbs, 1/4 cup granulated sugar, and melted butter. Mix until the crumbs are evenly moistened.

Press the mixture firmly and evenly into the bottom and up the sides of a 9-inch pie plate. Bake for 10-12 minutes, or until lightly golden. Let the crust cool completely on a wire rack while you prepare the fillings.

In a small saucepan, combine the huckleberries and 1/2 cup granulated sugar. Cook over medium heat, stirring occasionally, until the berries begin to break down and release their juices, about 5-7 minutes. If using frozen berries, they will release more liquid.

In a small separate bowl, whisk together the cornstarch and cold water until smooth. Pour the cornstarch slurry into the simmering huckleberry mixture. Continue to cook, stirring constantly, until the mixture thickens to a glossy, pudding-like consistency, about 1-2 minutes.

Remove from heat and stir in the lemon juice. Transfer the huckleberry filling to a clean bowl and let it cool completely to room temperature. This is crucial before assembling the pie.

In a large mixing bowl, using a hand mixer or stand mixer, beat the softened cream cheese until smooth and creamy. Add the powdered sugar and vanilla extract, continuing to beat until well combined and fluffy, scraping down the sides of the bowl as needed.

In a separate, chilled bowl, whip the cold heavy whipping cream until stiff peaks form. Gently fold the whipped cream into the cream cheese mixture until no streaks remain. Be careful not to overmix, as this can deflate the cream.

Once the graham cracker crust and huckleberry filling are completely cool, spread the huckleberry filling evenly over the bottom of the cooled crust.

Carefully spoon and spread the cream cheese layer over the huckleberry filling, smoothing the top with a spatula.

Cover the pie loosely with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow the pie to set properly.

Before serving, remove the pie from the refrigerator. Garnish with fresh huckleberries and additional whipped cream, if desired. Slice and serve cold.