In a medium saucepan, combine fresh cranberries, 1/2 cup sugar, and a splash of water and lemon juice. Cook over medium heat for about 10 minutes until the cranberries begin to burst and the mixture thickens.

While the cranberry mixture cools, sprinkle gelatin over 3 tablespoons of cold water in a small bowl and let it sit for 5 minutes to bloom.

Gently heat the cooled cranberry mixture until it's warm but not boiling. Stir in the bloomed gelatin until it fully dissolves.

In a large mixing bowl, whip the heavy cream with the remaining 1/2 cup sugar and a splash of vanilla extract until stiff peaks form.

Carefully fold the cooled cranberry-gelatin mixture into the whipped cream, using a gentle motion to preserve the airiness.

Once combined, pour the mousse mixture into the prepared graham cracker crust, smoothing the top with a spatula for an even finish.

When ready to serve, remove the pie from the refrigerator and garnish with freshly whipped cream, a sprinkle of powdered sugar, and a few fresh cranberries.