In a large mixing bowl, beat the heavy cream until medium peaks form.
In another large mixing bowl, beat together the cream cheese, peanut butter, and sugar until evenly incorporated. Add the vanilla and salt; mix to combine.
Add about 1/4 cup of the whipped cream to the peanut butter mixture. Use a rubber spatula to fold in the whipped cream until completely incorporated. (Do not skip this step! Doing this lightens up the peanut butter so it doesn't deflate the rest of the whipped cream.)
Add the rest of the whipped cream to the peanut butter mixture. Fold everything together until the peanut butter is light in color and no more white from the whipped cream is showing. Do not beat or stir, just keep folding. It's going to take a minute, but this process keeps the filling light.
Pour the filling into your prepared pie crust. Use the rubber spatula to spread the filling into an even layer, all the way to the edges of the pie crust.
Refrigerate for 2 hours.
Topping
Preheat your oven to 350 degrees F. Coat a small baking pan with non-stick cooking spray.
In a small mixing bowl, mix together the brown sugar and cinnamon.
Stir together the butter and vanilla. Pour over the brown sugar mixture and stir until everything is moistened.
Add the graham crackers pieces to the slurry and toss until coated.
Pour the graham crackers (and extra slurry) into your prepared baking dish. Sprinkle the top evenly with sugar and salt.
Bake for 15 minutes, or until lightly browned. Remove from the oven and cool completely.
Use a knife to chop the graham cracker into small pieces. Sprinkle the pieces over the center of your pie.