Preheat oven to 350 degrees. Press cookie dough into the bottom and up the sides of a lightly greased 9-inch pie plate.
Bake for 30 to 35 minutes. Let cool.
Place peanut butter in a large bowl with 1 cup of powdered sugar, 1/4 cup of water, and 2 tablespoons melted butter.
Beat with an electric mixer until smooth.
Gradually beat in the remaining 2 cups of powdered sugar.
Press the peanut butter mixture into the sugar cookie crust.
Combine chocolate chips and 4 tablespoons of butter in a small saucepan. Cook over low heat, stirring constantly, until melted. Pour over peanut butter mixture.
Chill for 1 hour to set the chocolate. Cut into wedges and serve with whipped cream if desired.