In a small saucepan or microwave, melt the peanut butter.
In a medium-sized bowl or a food processor, combine graham crackers, sugar, and melted peanut butter; blend until the texture of coarse meal.
Press into a 9- or 10-inch pie pan. Try to make the crust about 1/8 inch (1/3 cm) evenly all around. If the crumb mixture won't stick where you press them, just add another tablespoon of water to the mix. Even the crumbs up and make sure there are no gaps or holes. NOTE: If you chill the crust for an hour before you bake it, this will help prevent crumbling when you want to serve it.
Bake approximately 8 to 10 minutes. Remove from oven and let cool before filling. TIP: Before serving loosen pie crust from pan; dip bottom in hot water for a few seconds.
while the crust is cooling;
In a medium saucepan, combine butter and brown sugar. Cook over medium heat until butter is melted and mixture is smooth; stir frequently. Refrigerate 10 minutes.
In large bowl, beat peanut butter and brown sugar mixture at LOW speed until blended. Increase speed and beat 1 minute at HIGH speed. Reduce speed to LOW and add whipped topping; beat one additional minute.
Pour into graham crust and refrigerate for several hours before serving.